## a(n)=a(n−1)+gcd(n,a(n−1)).

Go ahead: Press the button. A number is printed on the tape. Press again and another number appears. Keep going. A few more. Notice anything special about those numbers? The sequence begins: 5, 3, 11, 3, 23, 3, 47, 3, 5, 3, 101, 3, 7, 11, 3, 13, 233, 3, 467, 3, 5, 3, . . .
posted by Wolfdog on Sep 6, 2015 - 25 comments

## Significand of the figure

From the somewhat arbitrary and dimensionful to the timeless classic, one man's subjective list of notable properties of specific numbers.
posted by Talkie Toaster on Nov 8, 2012 - 39 comments

## The On-Line Encyclopedia of Integer Sequences

Ever wondered what comes next, and why? The On-Line Encyclopedia of Integer Sequences has the answers. (Previously.)
posted by parudox on Mar 10, 2009 - 33 comments

## 3 is an odd prime, 5 is an odd prime, 7 is an odd prime, 9 is a very odd prime...

The Prime Game is not really much of a game, but it is a neat & little-known fact about the decimal representation of prime numbers.
posted by Wolfdog on Jul 10, 2007 - 24 comments

## Can you stump the Encyclopedia of Integer Sequences?

Can you stump the Encyclopedia of Integer Sequences? Every identifiable sequence known to man, including:

Name: Busy Beaver problem: maximal number of steps that an n-state Turing machine can make on an initially blank tape before eventually halting.
Comment: The sequence grows faster than any computable function of n, and so is non-computable.
Keywords: hard,huge,nice,nonn,bref

If your sequence does not appear there, you might want to try the Super Seeker.
posted by vacapinta on Apr 15, 2002 - 9 comments

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