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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.

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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 March 19

A119523: Decimal expansion of the van der Waerden–Ulam binary measure of the primes.

0.829365019702...
The formula is

k  = 1
χp(k)
2k  − 1
, where
χp(n)
is the characteristic function of the primes. The primes have a larger measure than the composites because they dominate the smaller integers.

The binary expansion of the van der Waerden–Ulam binary measure of the primes being obviously (see A010051)

0.1101010001010001010001000001010000010001010001...

The quaternary (base 4) expansion of the van der Waerden–Ulam binary measure of the primes being (see A??????)

0.31101101101001100101101...

In the quaternary expansion all the digits after the point, with the exception of the initial 3, are 0 or 1 since there is only one even prime.