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

1,1

Comments

Large terms correspond to probable primes.

a(34) > 50000.

Links

Table of n, a(n) for n=1..33.

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.

Example

10!3+243 = 10*7*4*1+243= 523 is prime, so 10 is in the sequence.

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

Crossrefs

Cf. A007661, A037082, A084438, A243078.

Sequence in context: A306929 A105140 A107018 * A048792 A024585 A190482

Adjacent sequences: A247865 A247866 A247867 * A247869 A247870 A247871

Keyword

nonn,more

Author

Robert Price, Sep 25 2014

Status

approved