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# OeisWiki:Community Portal

### From OeisWiki

## Contents |

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!)

- Motivation for the wiki
- Known things to do
- Known questions that need to be decided
- Road map for wiki migration
- System Status
- Information for new users
- FAQ

## Sequence of the Day for March 30

A121023: Multiples of 3 containing a 3 in their decimal representation.

- { 3, 30, 33, 36, 39, 63, 93, 123, 132, 135, 138, 153, 183, 213, 231, ... }

The graph of this sequence is (roughly) self-similar: it has the same appearance when the scale is multiplied by 10.

The same can be generalized to multiples of any other number *d* which have *d* as a substring in their decimal (or other?) expansion. Sequences A011531 (numbers having the digit 1) and A121022 through A121040 cover this for *d* = 1, ..., 20.

Another generalization is that of numbers containing some or all of their divisors as substrings in their decimal expansion, or simply the digits thereof. Relevant sequences include:

- A092911: All divisors can be formed using the digits of the number
- A239058: All divisors are a substring of the decimal expansion, which is the union of primes having a digit 1 (A208270) and the more challenging
- A239060: Non-prime numbers having all divisors are a substring of the decimal expansion (of which the 4th term is not yet known!)