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

Author

Robert Price, Aug 17 2014

Keywords

• nonn
• more

Comments

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

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

Examples

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

Links

• OpenPFGW Project, Primality Tester
• Henri & Renaud Lifchitz, PRP Records. Search for n!3-3

Crossrefs

Cf. A007661, A037082, A084438, A243078.

Programs

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

Extensions

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

a(35) from Robert Price, Oct 12 2014