A247465 Numbers n such that n!3 - 3^5 is prime.

10, 19, 28, 50, 67, 77, 89, 112, 139, 146, 184, 194, 233, 310, 311, 388, 886, 1139, 1648, 1694, 2405, 2554, 3709, 4015, 5410, 5908, 6407, 8065, 9061, 9875, 11722, 13471, 26026, 26656, 29441, 32741

Offset: 1

Author

Robert Price, Sep 17 2014

Keywords

• nonn
• more

Comments

Large terms correspond to probable primes.

a(37) > 50000.

Examples

			10!3-243 = 10*7*4*1-243 = 37 is prime, so 10 is in the sequence.
		

Links

• Henri & Renaud Lifchitz, PRP Records. Search for n!3-243
• 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] - 243], AppendTo[lst, n]], {n, 100}];lst