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This page contains notes about the status of the OEIS wiki. It provides a brief description of the wiki setup. It will also be used to announce changes in the structure of the wiki, so it may be useful to add it to your watchlist by clicking on the watch tab at the top of the page.

Users can create and modify discussion pages here. The discussion pages are a reasonable place to make comments about the structure of the wiki.

Do not use the discussion pages to suggest changes to OEIS sequence entries.

An account is necessary to contribute to the Wiki. To request an account, click here. There was a time when the username was required to be your Real Name. This is no longer required, but is strongly recommended. If this evolving statement causes you to want to change your username, send email to David, and I can make the change.

A few preliminary pages (most of these need to be updated!)

Sequence of the Day for August 20

A053169:
n
is in this sequence if and only if
n
is not in sequence A 
n
in the OEIS database.
{ 4, 7, 9, 11, 12, 13, 15, ... }

The number 40 is definitely not a prime number, yet in the OEIS it is the A-number that indexes the prime numbers (see A000040). Since early on, contributors to the OEIS have been interested in this kind of question. Since A-numbers are generally assigned by computer, and the computer has no directive to try to choose an A-number that would be “appropriate” or “ironic” for a given sequence, it is almost a matter of luck whether a new sequence will get an A-number that is in the sequence itself.

Here’s two puzzles for the day:

  1. Should the number 51369 be in A053169? (Welcome to Russel’s paradox!)
  2. Should the number 0 be in A053169? (Daniel Forgues had suggested using A000000 for the empty sequence, and Neil Sloane was amenable to the idea, but since that sequence has no terms, the lookup programs would not be able to handle it.)

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* See On-Line Encyclopedia of Integer Sequences#Self-referential sequencesWikipedia.org.