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

1,1

Comments

Large terms correspond to probable primes.

a(29) > 50000.

Links

Table of n, a(n) for n=1..28.

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.

Example

7!3 + 81 = 7*4*1 + 81 = 109 is prime, so 7 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] + 81], AppendTo[lst, n]], {n, 100}]; lst

Crossrefs

Cf. A007661, A037082, A084438, A243078.

Sequence in context: A331703 A032537 A072120 * A057126 A363026 A319250

Adjacent sequences: A247863 A247864 A247865 * A247867 A247868 A247869

Keyword

nonn,more

Author

Robert Price, Sep 25 2014

Status

approved