A247868 Numbers n such that n!3 + 3^5 is prime, where n!3 = n!!! is a triple factorial number (A007661).

7, 10, 11, 22, 23, 25, 44, 46, 47, 50, 53, 55, 89, 122, 214, 410, 427, 526, 539, 575, 1369, 1370, 2291, 4999, 5374, 7202, 7375, 7823, 8921, 9764, 22967, 25507, 44117

Offset: 1

Author

Robert Price, Sep 25 2014

Keywords

• nonn
• more

Comments

Large terms correspond to probable primes.

a(34) > 50000.

Examples

			10!3+243 = 10*7*4*1+243= 523 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