A247464 Numbers n such that n!!! - 3^4 is prime.

10, 13, 14, 17, 20, 26, 29, 31, 32, 50, 59, 77, 82, 104, 164, 185, 217, 263, 293, 361, 437, 442, 545, 547, 599, 608, 623, 739, 782, 1081, 1120, 1138, 1429, 2516, 2518, 4277, 4529, 5438, 5596, 11945, 12716, 13955, 14540, 31730, 31769, 42964, 46396

Offset: 1

Author

Robert Price, Sep 17 2014

Keywords

• nonn
• more

Comments

Large terms correspond to probable primes.

a(48) > 50000.

Examples

			10!3-81 = 10*7*4*1-81 = 199 is prime, so 10 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