QandA For New OEIS

Questions and Answers Page for the New OEIS

This page is intended for public discussions of problems, improvements, etc. related to the new OEIS! Please sign anything you enter here. Unsigned entries were written by N. J. A. Sloane (njasloane@gmail.com).

The OEIS brain now has two halves, the database http://oeis.org and the Wiki http://oeis.org/wiki

• The main OEIS page is now http://oeis.org. Use that page for looking up a sequence, searching the database, contributing new sequences, editing sequences, etc.
• The OEIS Wiki contains discussion pages related to the OEIS – everything EXCEPT the sequences themselves. Before contributing to the OEIS, you must first register with the Wiki.
• Important: the two halves of the brain require separate logins! But your user name and password are the same for both halves.
• Because of problems with spam, new users can contribute to the OEIS, but not to the OEIS Wiki. After a user has made some meaningful contributions to the OEIS they can request editing access to the OEIS Wiki (by sending a request to the OEIS administrators).
• In other words, there are two halves to the oeis.org brain: the main OEIS (at http://oeis.org) which contains all the sequence data, and the Wiki (at http://oeis.org/wiki) which contains auxiliary information. — David Applegate, Nov 12, 2010
• The old OEIS web sites (www.research.att.com/~njas/sequences/ and oeis.org/classic) are now defunct.
• The Special Pages page in the Wiki has links to several useful files, such as the list of registered users.

You can use the OEIS without registering

• Just go to the main OEIS site at http://oeis.org.
• No content is hidden from non-registered users.
• Of course there is no charge for using the OEIS.

Registering

• Please remember that to edit an existing sequence or to contribute a new sequence, you must first register with the OEIS Wiki. Then use the same user name and password for the main OEIS page.
• When you go to the registration page, you start by entering your full name in the top two windows, then your email address, etc. When you have received a password, you can go the main OEIS site at http://oeis.org, click the login button at the top right corner, and then log in with the same user name and password.

The two license agreements

• Q. What are the license agreements?
• A. There are two primary documents, in plain text, which are part of the Terms of Service agreed to when requesting an account on the OEIS. Neither is in PDF.
• These are The OEIS End-User License Agreement, linked to at the bottom of every page, and The OEIS Contributor's License Agreement, linked to at the top of the OEIS edit page, and at the bottom of the Wiki edit page.
• You can also see them directly at The OEIS End User License Agreement and The OEIS Contributor's License Agreement

Editing an existing entry

• If you are logged in as a registered user, just under the Data of each sequence, next to the "history" link, you will see an "edit" link. Use this to propose edits to the sequence (new terms, new references, etc). Unregistered users do not see the "edit" link.
• If two people are editing a sequence at the same time, if the edits are in disjoint sections of the page, both will take effect. If the edits are in the same section, the second person will get a warning and will have the opportunity to combine the edits.
• If we see a lot of bad edits by someone, we can remove their name from the list of registered users. Let one of the Editors-in-Chief know if you see a need for this.
• Q. I observed that no preview of the contributions is longer possible. Did I miss something? I always regarded it as a very useful aid.
• A. If you click "hide guide text" you should find that the page is essentially an editable preview (except for the hyperlinks), which is even more useful than clicking back and forth. It is also perfectly acceptable to save changes, remember something else, and click edit again.

The "Undo Changes" button

• Clicking the "I want to undo these changes" button will undo the last change that was made to the entry, WHETHER OR NOT IT WAS YOUR CHANGE!
• So this is an exception to the rule that only editors can make changes!
• Please be very careful when using this button!
• The reason the button is set up this way is so that anyone can undo their own mistakes. But it can be misused. Be careful!

I can't see the "Add note ..." window

• Sometimes, if a line is very long, the "Add note ..." window may be a long way to the right on the screen. Look for a horizontal scroll bar at the bottom of the screen!

Format for contributions

• Note that in the internal format for sequences, each line begins with %I, %S, %N, etc., as before, but the A-number no longer appears in the second field.
• Q. On the wiki, TeX can be used and makes the reading of formulas much easier. Does the sequence database already support TeX? Even if it is not supported yet, is it reasonable to use it with regard to a support in the future?
• A. Please don't use TeX yet in the sequence database. The format is still the same as it was. The only thing we've changed yet is the ability to edit.

About the Offset: When is a sequence a list?

Question: I am almost always confused about what is, and what isn’t, a “list” for OEIS purposes, and that in turn makes me almost always uncertain about what the proper offset should be. In Mathematica, every sequence in the OEIS is a “list,” and the dictionary (not-necessarily-mathematical) definition of a “list” is “a number of connected items or names written or printed consecutively . . . .” Eric Weisstein’s definition in the CRC Concise Encyclopedia of Mathematics is a “data structure consisting of an ordered set of elements, each of which may be a number, another list, etc.” So far as I now understand those definitions, both the Dictionary and the Weisstein definitions would properly describe each and every sequence in the OEIS. What are the criteria by which one could say that A is a list but B is not a list for purposes of the OEIS?

Answer: "a(n) = n^2" is a function or formula and the offset is the initial value of n.

Numbers n such that n is prime is a list and has offset 1

If the definition says "Numbers with the following property" that is a list

Another clue: if the definition says what the n-th term is, that is a function not a list. But if it says what the numbers are, that is a list!

Question (continued): Thanks for your message. I remain slightly confused. Let me illustrate. For conciseness, I’ll refer to each of your email’s paragraphs by its number, e.g., the rule that “n^2 is a function or formula and the offset is the initial value of n” is in your first paragraph and I’ll call it “rule 1.”

Here are some examples: the definition says “a(n)=n^2.” By your rules 1 and 3, that is not a list. But if the definition is “numbers n such that n is the least square not already used, starting with 1,” by your rule 2, then that is a list? Or if the definition is “numbers with the property that each is the smallest square greater than its predecessor,” is that, by virtue of your rule 4, a list? Does classification as a list or not a list depend on how the definition is worded?

Here is another example: the definition says “the n-th term is the product of all positive integers equal to or less than n,” then that is a function (and not a list) per your rule 5, but if the definition says “the factorials,” then, again by your rule 5, that is a list?

I hope you can see my confusion, and I apologize if I’m being dense.

Answer (continued): I'LL INTERPOLATE MY RESPONSES IN CAPS

Here are some examples: the definition says “a(n)=n^2.” By your rules 1 and 3, that is not a list. YES But if the definition is “numbers n such that n is the least square not already used, starting with 1,” by your rule 2, then that is a list? YES Or if the definition is “numbers with the property that each is the smallest square greater than its predecessor,” is that, by virtue of your rule 4, a list? YES Does classification as a list or not a list depend on how the definition is worded? OF COURSE [a(n)=n is not a list. "The natural numbers" is a list. Same sequence, described in two ways. If is is a function of n, it is not a list. But if is described as numbers with some property, then it is a list]

Here is another example: the definition says “the n-th term is the product of all positive integers equal to or less than n,” then that is a function (and not a list) per your rule 5, YES but if the definition says “the factorials,” then, again by your rule 5, that is a list? YES

IT IS a bit like the difference between the view from inside the sequence - the functional definition , not a list - and the view from the outside by an external observer, when it becomes a list.

Question (continued): Thanks — that helps a lot. I was trying to figure out, by looking at the terms of the sequence, whether it constituted a list or not. Now I understand that I should be looking at the definition or description, rather than the terms, to make that distinction.

Should I sign my contributions? (Yes!)

• Q. When I add something to an entry, should I sign my name?
• A. Yes, and add the date.
• For example, if you are adding a formula, do something like this:
  • a(n) = ... . - ~~~~     which yields something like "... - J. Smith, Dec 21 2010"
    • NOTE: the 4 tildas will be expanded to your "hyperlinked" name and appended date. The hyperlinking (to the wiki userpage) can also be done by hand by surrounding the name (take care of exact spelling) with underscores, i.e.: _J. Smith_.
  • IMPORTANT: Do that only if you have a proof that the formula or comment or program, etc., is correct. Otherwise you must say:
  • It appears that a(n) = ... . - _J. Smith_, Dec 21 2010
  • Just because a formula matches the first thousand terms does not prove that it is correct.
• If you are adding more terms just to fill up the 260 characters (see guide text), or three lines of the internal format, and the reader can easily check the terms and compute further terms using the information given in the entry, then you should NOT sign.

• Q. So searching for

extension:"extended by" keyword:easy -extension:corrected

should return (almost) no results from the current epoch?

This could not be made retrospective, because easy extensions from the previous epoch cannot be seen in the history tab?

--Jason Kimberley 03:58, 13 January 2011 (UTC)

• If however you are correcting one or more terms, or if new terms are produced by application of some non-elementary theory, by a sophisticated algorithm or if they simply require a few hours or days of cpu-time, then attribution is desirable and necessary, and you should write something in the Extensions section, such as:
  • a(5) and a(14) corrected. - J. Smith, Dec 21 2010
  • a(12)-a(17) computed using ... (see comment above). - J. Smith, Dec 21 2010
• Signing your name to contributions is important because this is a scientific database, and everything must be documented. (It is true that the History tab shows who contributed what, but for the big entries it is hard to sort through all the History entries, and in any case it is much more convenient to have the signature visible after the contribution.)
• This applies to comments, formulas, programs, even cross-references and examples in highly non-trivial cases. Everything except the Data lines, where there is no way to add signatures (use the Extensions line in those cases)
• However, links and references should normally not be signed.

Using a draft prepared in advance to create a new entry

• Q. I like to create a text file on my machine and then copy&paste it into a new sequence entry. But when I do that all the lines end up in the same window.
• A. What you should do is edit the internal format. Go to Edit / Edit internal format. Then use the mouse to insert the text file. Then prefix each line with the appropriate symbol (%N, %S, %C, %p, etc.) Alternatively, copy&paste each section separately.

Does the OEIS allow nonascii characters?

• Q. Does the OEIS allow nonascii characters? What about accents, Greek letters, math symbols, superscripts, subscripts, etc.?
• A. Roughly speaking, the answer is No to all of these.
• The OEIS is in UTF-8, like most of the Internet. We have no plans to support other character sets.
• So please do not use things like the superscript "little 2" to mean "squared" (use ^2 instead), the Greek letter "pi" for 3.14159... (use Pi instead), or other Greek letters.
• However, some accents are permitted in names (Olivier Gérard, for example).

Which text editor should I use?

• Q. Could someone using Windows OS suggest a text editor that allows one to save files using UTF-8? (The uploader expects text files to be encoded in UTF-8.)
• A. 1. As an occasional Windows user, I like the freeware Notepad++ available from Sourceforge: http://notepad-plus-plus.org/.
• Notepad++ supports conversion to UTF-8 of old IBM/MS Codepages and this comes in handy when dealing with old notes and documents typed by people in one of the many systems for cyrillic. It keeps a list of files open in previous sessions and makes them readily accessible.
• A. 2. Use Textpad http://www.textpad.com.
• Textpad is the best text editor for windows that I know. You can save the text file in many formats: PC, Unix, Mac, ANSI, UTF-8, etc.

Format for References and Links

• References should be listed in alphabetical order by author's last name.
• Links should be listed in alphabetical order by author's last name, except that a link to the b-file, if there is one, comes first, and any links to the Index or links without authors' names come at the end.
• If you see references or links that are out of order, please use the "edit" button and put them in order.

Hyperlink shown in plain text, not active link

• Q. Why is the hyperlink is shown in plain text instead of being a link?
• A. You put it in the wrong place - hyperlinks should go in the "Links" section, not in the "References" section!

Hyperlink does not appear

• Q. I unsuccessfully tried several times to add to A181595 the following link:

V. Shevelev, <a href=http://arxiv.org/abs/1011.6160>On perfect and near-perfect numbers</a>

Changes are saved, but after that in "history" I do not find them.

• A. You left out the quotation marks! It should be:

V. Shevelev, <a href="http://arxiv.org/abs/1011.6160">On perfect and near-perfect numbers</a>

What should I do about a broken link?

• Q. I found a broken link. What should I do?
• A. First add "[Broken link?]" at the end of the line.
• There are several reasons why links break, so there are several things you can do next:
  • The author forgot to pay his bill. The link may be working again next month.
  • The URL changed. See if you can find out where it moved to. Search the web or ask the author.
  • The page may no longer be of interest. The link can probably be deleted.
  • The page was important, but does not exist any more. In that case it can usually be retrieved from the Web Archive. Use archive.org. Take the address, and put this in front of it:

http://web.archive.org/web/*/

For example, to search for a missing web page called

http://alpha.ujep.cz/~vicher/puzzle/polyform/dude/pentdude.htm

you would enter

http://web.archive.org/web/*/http://alpha.ujep.cz/~vicher/puzzle/polyform/dude/pentdude.htm

then you just pick the version you want. When we find the missing page, if it is sufficiently important, we will ask the author for permission, and then put a cached copy on the OEIS web site. See A076335 for an example.

Uploading b-files, figures, etc.

• Q: Is it possible to submit b-files or other files associated with a sequence?
• A: Yes! See Contributing a b-file or other file to the OEIS. To find this page, click on the "Contribute new seq. or comment" link at the bottom of any OEIS page.

• Q: Does the system check to see if the b-file matches the present terms?
• A: Yes! Both the offset and the initial terms must match what is in the entry, or you will receive an error message. If the entry happens to be wrong, that has to be corrected before you can upload the b-file. However, this does not work the other way: if you change the Data and there is an existing b-file, you will get no warning.

Uploading illustrations

• Q. How do I upload an illustration for a sequence? I have been working on A182840. A byproduct of that are the asci graphs I have put on my user talk page for now: http://oeis.org/wiki/User_talk:Olaf_Vo%C3%9F
• A. You can add them to the supported files in A182840 by saving the ASCII graphs in a file, say graph.txt, and then going to edit A182840 (the sequence). In the Links section, click "I want to upload a supporting file" and then find the file graph.txt using the file chooser and edit the new link line.

Problems with minus signs

• If the sequence contains negative numbers, e.g. 1, -2, 3, -4, 5, ..., include them just as you would positive numbers.
• The lookup search generally ignores minus signs.

A-numbers and how long they will last

• A-numbers are the absolute, permanent ID numbers (or catalog numbers) used for sequences
• They will never change (although in 25 or so years we may have to go to eight-digit numbers, which should be adequate for the next thousand years)
• See A-numbers for further information.

Reserving a block of A-numbers

• Q. How do I reserve a group of adjacent A-numbers?
• A. At the foot of any OEIS page, click on "Contribute new seq. or comment", and see the link in Section 1.

Seeing which A-numbers have been reserved but not yet used

• You can list all allocated A-numbers by searching for

keyword:allocated

• You can search for your allocated A-numbers by searching for example for

keyword:allocated name:"allocated for M. F. Hasler"

Creating a sequence if you have been allocated an A-number

• Enter the A-number in the search box, click "Edit", and enter the information.

Looking at recent additions and changes to the OEIS

• You can do a search for "keyword:new" or for a particular date, say "Nov 14 2010". See the hints file for further information.
• Or, use the WebCam, and set it to Recent Additions
• The old file "recent.txt" no longer exists.

Why did my sequence disappear?

• Q. I submitted a sequence, but now I can't find it and the A-number has been recycled. What happened?
• A. There are several possible reasons why this might have happened. See Deleted sequences.

Sequences declared "dead"

• Q. On what conditions is a duplicate declared dead instead of being recycled?
• A. Generally this happens when the sequence has been in the OEIS for several years. Sequences could also be created "dead", if an erroneous sequence is found in the literature.

Updating the old pages

• A lot of work needs to be done still.
• Most of the old pages like the Welcome page, More page, the Puzzle page, etc., have links that don't work any more. I am in the process of editing these pages!
• The pfr page is unimplemented, likely for a while. — Russ Cox 14:24, 16 November 2010 (UTC)

Sending email to an author or editor

• Provided this person has a user page on this Wiki (and ideally every contributor should have such a page), first go to the OEIS Wiki (https://oeis.org/wiki), login in the upper right corner, then go to the user's page (enter, for example, User:John Doe, in the Wiki search box). Then there should be a link in the Toolbox on the left saying "E-mail this user". Of course, there are many possible reasons why a contributor, even one with a user page, may not have a current email address.

I strongly support the idea that all contributors should have a "user page". To avoid flooding this page, I will elaborate on this point on the talk page. — M. F. Hasler 12:30, 15 November 2010 (UTC)

What does "mod n" mean?

• A lot of contributors to the OEIS find this confusing. Note that

a == b (mod c)

means that a-b is a multiple of c.

So 12 == 8 (mod 2).

But

a mod c = b

means that the remainder when a is divided by c is b.

So 12 mod 2 is 0, not 8.

Grouping of a formula or expression

• Q. Which of (), [], {}, <> are allowed in an expression for grouping (overrule operator precedence)?
• A. There is (still) no general agreement on that. Recommendation: Use only ().

Searching for a sequence that contains certain terms

• Q. Has any thought been given to including "wild-card" characters in the search? For example, 12, 22, 36, *, 100. This would allow searching for sequences when not all the input terms are known.
• A. Yes, there are "_" and "__" wildcards, and you can also try searching for a subsequence. See the Hints page for further information.

Searching for a sequence that BEGINS with certain terms

• Q. I am unable to find sequences starting with a given number, for example with the numbers 55,76 and nothing else on the left.
• A. Download a copy of the compressed list of just the sequences and A-numbers, from https://oeis.org/wiki/Welcome#Compressed_Versions (see the Welcome Page on the OEIS Wiki). Then uncompress it and search for " 55,76," with the initial space.

• Q. Is it possible to list sequences that start with let's say 1 and have a second number that is greater than let's say 2500?
• A. The sequences are arranged lexicographically, so that is easy.

First find a sequence that starts 1,2500 by searching for 1,2500.

You discover A062120 = 1, 2500, 3600, 62500,...

Go to that entry: https://oeis.org/A062120

Look at the sequence-in-context line:

Sequence in context: A252315 A131523 A307764 * A220025 A253377 A253370

From here you can walk through all the sequences that start 1, 2501, ... and so on (click the numbers to the right of the asterisk; repeat the procedure)

URLs for sequences in the new OEIS

• The URL for a sequence in the OEIS is (for example) https://oeis.org/A123456
• When referring to a sequence in a page on the OEIS wiki, just say (for example) A123456. This will automatically become a link to the entry. [Don't use the old templates, they are obsolete and just slow things down.]

• Q. Should I now change all my links to sequences from e.g., http://www.research.att.com/~njas/sequences/A001113

to https://oeis.org/A001113 ?

• A. Yes!

The files stripped.gz, names.gz

• Q. What happened to the compressed files stripped.gz and names.gz?
• A. Their new names are http://oeis.org/stripped.gz and http://oeis.org/names.gz. They are updated daily.
• Remember that their use is governed by The OEIS End User License Agreement

How do I get a blank starting page?

• Q. When I go to the OEIS main page, there is a sample sequence already filled in. Is it possible to get a blank version of this page?
• A. Use http://oeis.org/?blank=1. — Russ Cox, Jan 04 2011

Login problems

• Q. My password doesn't work!
• A. Passwords and accounts are managed by the wiki. Use the wiki login page to request a new temporary password, and to log in using a temporary password and change it to a permanent one. The steps to reset a password are:

1. Go to the wiki login page.
2. Click on "E-mail new password".
3. Wait for the email containing your new temporary password.
4. Go back to the wiki login page.
5. Log in using the temporary password contained in the email.
6. The wiki will require that you change the password. Follow the prompts to change to a permanent password.
7. You can now use this permanent password to log in on the main OEIS login page.

• Q. How do I change my password?
• A. Use Special:ChangePassword.

How can I suggest or ask about server features?

• Q. How can I suggest or ask about server features?
• A. The wiki page User:Russ_Cox/OEIS_Server_Features contains a list of planned and suggested changes.

Numbers appearing next to the Name of a sequence

• Q. What do the two little numbers next to the Name of a sequence mean (On the right hand side of the Name, they are aligned vertically. One is signed "+" while the other has no sign)?
• A. See the paragraph "The meaning of the little numbers at the right of the blue bar" at the bottom of the Hints page.

New user with existing contributions

• Q. I've just created an account, however I already have some 100 contributions, all of them having an old email address with them. I would like to have the email addresses removed, and my name linked to my wiki account, just like other users. Do I have to change each entry manually, or is there some automated process for this?
• A. Normally this can be easily done by one of the bureaucrats with a simple global edit. Ask admin@oeis.org for help.

What to do when there are too many cross-references in a sequence

• A. When there are too many cross-references, make an entry in the Index to the OEIS, and replace the list of cross-references with a link to that page on the Index. Example: "Index entries for sequences related to Benford's law" which you can see at the bottom of the links in A000040

Why are my submissions taking so long to be accepted?

See: Why are my submissions taking so long to be accepted

Why am I limited to 3 submissions?

See: Why am I limited to 3 submissions

What if I have an idea for new sequences?

See: What if I have an idea for new sequences

I can prove one of the conjectures, what should I do?

• Answer: Usually you would change "Conjecture" to "Theorem", and give the proof, like this:

• Instead of: Conjecture: a(n) = (3240 + 10158*n + 11777*n^2 + ....). - _Colin Barker_, Apr 09 2013

you would change it to:

Theorem: a(n) = (3240 + 10158*n + 11777*n^2 + ....). [Conjectured by _Colin Barker_, Apr 09 2013]

Proof: [From _Your name_, Jun 12 2019]

Give proof (or a sketch of the proof. QED

How to access the OEIS from a cell phone

Answer: People tell me that accessing the OEIS from a cell phone works just fine.

For example, one of the editors-in-chief says: oeis.org works fine in the Safari browser which is part of the iPhone. I rotate the phone into the horizontal "landscape" position. Find the search box and type in the numbers you're searching for, and hit the blue "GO" button (which is where the return key would be on the keyboard) and it does the search.

I am interested in becoming a volunteer OEIS editor. What should I do?

• Answer: Thank you for your interest. Indeed, we are always looking for new editors because there is a lot to be done on the pile of submissions. However, unless you are very familiar with the OEIS editing process, it is a little early to apply for this position.

• In addition to mathematical knowledge, which we trust you to have, you also need experience with the procedures and conventions of the OEIS.

• We suggest you monitor this page: https://oeis.org/draft. At first only read the contents, and then later you can consider adding your own comments to the drafts. One way or another, you will then get feedback.

• And when experienced editors have noticed you, it could be that they decide one day to make you an editor. However, there is no formal procedure for this.

• Good luck, see you on the draft page!

Questions and Answers for the Wiki Half of the OEIS Brain

Wiki terminology

I find the MediaWiki terminology sometimes confusing.

"Flagged" means "approved", "stable version" means "official version".

Fonts in Wiki

Is it possible to use a fixed-width font on wiki pages?

Yes, there are several ways to get monospace fonts on the wiki.

Method 1

Use <pre>…</pre> tags around blocks of text.

For example:

<pre> This is the first line of a block of text enclosed in "pre" tags. This is the second line of a block of text enclosed in "pre" tags. </pre>

produces the following result:

This is the first line of a block of text enclosed in "pre" tags. This is the second line of a block of text enclosed in "pre" tags.

Method 2

Use <code>…</code> tags around text.

For example:

This is a line of text with <code>this piece</code> enclosed in "code" tags.

produces the following result:

This is a line of text with this piece enclosed in "code" tags.

Method 3

It is possible to use "code" tags around blocks of text, but multiple spaces and single newlines will be suppressed in this case. Additional spaces and newlines may be forced through the use of HTML "non-breaking space" and <br> codes.

For example:

<code> This is the first line of a block of text enclosed in "code" tags.<br> This is the second line of a block of text enclosed in "code" tags.<br> </code>

produces the following result:

This is the first line of a block of text enclosed in "code" tags. This is the second line of a block of text enclosed in "code" tags.

Method 4

Use <math>\texttt{…}</math> if you want LaTeX.

See examples here: [1].

Method 5

Use a space character before each line of text.

For example the contents of this box (without the quotes):

" "This is the first line of a block of text with spaces before each line of the source. " "This is the second line of a block of text with spaces before each line of the source.

produces the following result (including the box):

This is the first line of a block of text with spaces before each line of the source. This is the second line of a block of text with spaces before each line of the source.

Pages and categories named after living people

Only [[User:Username]] pages created for registered users of OEIS Wiki, otherwise pages and categories named after living people are not appropriate in OEIS Wiki. — Daniel Forgues 03:34, 14 February 2011 (UTC)