A242994 Numbers n such that n!3 - 3 is prime, where n!3 = n!!! is a triple factorial number (A007661).

5, 10, 11, 13, 16, 22, 28, 71, 74, 94, 119, 121, 134, 157, 200, 262, 286, 484, 1039, 1045, 1190, 1595, 1679, 1772, 1789, 2410, 2920, 5039, 7919, 10462, 11846, 23293, 26705, 30781, 43694

Offset

1,1

Comments

Large terms correspond to probable primes. - Jens Kruse Andersen, Aug 19 2014

a(36) > 50000. - Robert Price, Oct 12 2014

Links

Table of n, a(n) for n=1..35.

OpenPFGW Project, Primality Tester

Henri & Renaud Lifchitz, PRP Records. Search for n!3-3

Example

11!3-3 = 11*8*5*2-3 = 877 is prime, so 11 is in the sequence. - Jens Kruse Andersen, Aug 19 2014

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
lst={}; Do[If[PrimeQ[MultiFactorial[n, 3] - 3], AppendTo[lst, n]], {n, 100}]; lst

Crossrefs

Cf. A007661, A037082, A084438, A243078.

Sequence in context: A134002 A028760 A028807 * A070791 A173901 A016084

Adjacent sequences: A242991 A242992 A242993 * A242995 A242996 A242997

Keyword

nonn,more

Author

Robert Price, Aug 17 2014

Extensions

Links and crossrefs fixed by Jens Kruse Andersen, Aug 19 2014

a(35) from Robert Price, Oct 12 2014

Status

approved