First q: x tells you that all elements of x are prime. Then _1 p: x tells you the indices of the primes, and the indices are readily recognizable as a sequence.
----- Original Message ----- From: Kip Murray <[email protected]> Date: Monday, August 17, 2009 12:01 Subject: Re: [Jprogramming] Takes from a mystery sequence To: Programming forum <[email protected]> > Part two: If you used J to help you figure out the sequence, tell > > Kip Murray wrote: > > Verb i. produces takes from the sequence of non-negative integers: > > > > i.20 > > 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 > > i.5 > > 0 1 2 3 4 > > 5 {. i.20 > > 0 1 2 3 4 > > > > Verb s generates takes from a mystery sequence (no peeking in > Sloane, please) > > > > s 13 > > 2 3 7 19 53 131 311 719 1619 3671 8161 17863 38873 > > s 5 > > 2 3 7 19 53 > > 5 {. s 13 > > 2 3 7 19 53 > > > > Your mission, should you decide to accept it, is to provide a > definition for s . > > As always, these instructions will ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
