A242516 Numbers n such that k!/n is prime for some k.

1, 2, 3, 8, 12, 24, 40, 60, 144, 240, 360, 720, 1008, 1680, 2520, 5760, 8064, 13440, 20160, 51840, 72576, 120960, 181440, 518400, 725760, 1209600, 1814400, 3628800, 5702400, 7983360, 13305600, 19958400, 43545600, 68428800, 95800320, 159667200, 239500800, 479001600, 566092800

Offset

1,2

Comments

This sequence is the union of the sequences {n!/p: p | n! and p is prime}. Thus this sequence is infinite.

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..1000

Prog

(PARI)
a(n)=for(k=1, n+2, s=k!/n; if(floor(s)==s, if(ispseudoprime(s), return(k))))
n=1; while(n<10000, if(a(n), print1(n, ", ")); n++)
(PARI)
v=[]; for(n=1, 50, forprime(p=1, n, v=concat(v, n!/p))); vecsort(v) \\ faster program

Crossrefs

Cf. A242457.

Sequence in context: A303851 A218542 A194452 * A282281 A321175 A079980

Adjacent sequences: A242513 A242514 A242515 * A242517 A242518 A242519

Keyword

nonn

Author

Derek Orr, Aug 16 2014

Status

approved