A247886 Numbers n such that n!3 + 3^3 is prime.

2, 4, 5, 8, 10, 11, 14, 20, 23, 32, 34, 46, 47, 62, 136, 179, 208, 209, 229, 311, 340, 406, 692, 1235, 1349, 2558, 2651, 2873, 3794, 7417, 8647, 8695, 10004, 13595, 18658, 21427, 23120, 43316

Offset: 1

Author

Robert Price, Sep 25 2014

Keywords

• nonn
• more

Comments

Large terms correspond to probable primes.

a(39) > 50000.

Examples

			10!3+27 = 10*7*4*1+27= 307 is prime, so 10 is in the sequence.
		

Links

• Henri & Renaud Lifchitz, PRP Records. Search for n!3+27
• Joe McLean, Interesting Sources of Probable Primes
• OpenPFGW Project, Primality Tester
• Eric Weisstein's World of Mathematics, Multifactorial.

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] + 27], AppendTo[lst, n]], {n, 100}];lst