A139202 Numbers k such that (k!-7)/7 is prime.

7, 9, 20, 23, 46, 54, 57, 71, 85, 387, 396, 606, 1121, 2484, 6786, 9321, 11881, 18372

Offset

1,1

Comments

a(19) > 25000. - Robert Price, Nov 05 2016

Links

Table of n, a(n) for n=1..18.

Mathematica

a = {}; Do[If[PrimeQ[(n! - 7)/7], Print[a]; AppendTo[a, n]], {n, 1, 300}]; a (*Artur Jasinski*)

Crossrefs

Cf. A139189, A139190, A139191, A139192, A139193, A139194, A139195, A139196, A139197, A139198.

Cf. n!/m-1 is a prime: A002982, A082671, A139056, A139199-A139205; n!/m+1 is a prime: A002981, A082672, A089085, A139061, A139058, A139063, A139065, A151913, A137390, A139071 (1<=m<=10).

Sequence in context: A074343 A103853 A192160 * A243996 A125968 A147068

Adjacent sequences: A139199 A139200 A139201 * A139203 A139204 A139205

Keyword

hard,more,nonn

Author

Artur Jasinski, Apr 11 2008

Extensions

More terms from Alexis Olson (AlexisOlson(AT)gmail.com), Nov 14 2008

a(13)-a(14) PRPs from Sean A. Irvine, Aug 05 2010

a(15)-a(18) PRP from Robert Price, Nov 05 2016

Status

approved