A247866 Numbers k such that k!3 + 3^4 is prime.

2, 7, 14, 16, 22, 23, 26, 40, 43, 47, 58, 62, 70, 107, 265, 292, 439, 874, 982, 1063, 1150, 2506, 3578, 3775, 7679, 10024, 42625, 46714

Offset: 1

Author

Robert Price, Sep 25 2014

Keywords

• nonn
• more

Comments

Large terms correspond to probable primes.

a(29) > 50000.

Examples

			7!3 + 81 = 7*4*1 + 81 = 109 is prime, so 7 is in the sequence.
		

Links

• Henri & Renaud Lifchitz, PRP Records. Search for n!3+81
• 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] + 81], AppendTo[lst, n]], {n, 100}];lst