A139200 - OEIS

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A139200

Numbers k such that (k!-5)/5 is prime.

3

5, 11, 12, 16, 36, 41, 42, 47, 127, 136, 356, 829, 1863, 2065, 2702, 4509, 7498

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

a(16) > 3000. - Ray G. Opao, Oct 05 2008

a(18) > 25000. - Robert Price, Nov 20 2016

LINKS

Table of n, a(n) for n=1..17.

MATHEMATICA

a = {}; Do[If[PrimeQ[(n! - 5)/5], Print[a]; AppendTo[a, n]], {n, 1, 300}]; a (* Artur Jasinski *)

PROG

(Magma) [n: n in [5..500] | IsPrime((Factorial(n)-5) div 5)]; // Vincenzo Librandi, Nov 21 2016

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: A122955 A030318 A102175 * A102181 A103068 A277136

Adjacent sequences: A139197 A139198 A139199 * A139201 A139202 A139203

KEYWORD

hard,more,nonn

AUTHOR

Artur Jasinski, Apr 11 2008

EXTENSIONS

a(13)-a(15) from Ray G. Opao, Oct 05 2008

a(16) from Serge Batalov, Feb 18 2015

a(17) from Robert Price, Nov 20 2016

STATUS

approved