A291349 Numbers k such that k!4 + 2^8 is prime, where k!4 = k!!!! is the quadruple factorial number (A007662).

1, 7, 11, 31, 57, 73, 97, 105, 209, 245, 403, 545, 917, 953, 1177, 1239, 1283, 1627, 2465, 3701, 4479, 4637, 6349, 7983, 11155, 13595, 15547, 17031, 17609, 24087, 24707, 39773, 40407, 63329

Offset: 1

Author

Robert Price, Aug 22 2017

Keywords

• nonn
• more

Comments

Corresponding primes are: 257, 277, 487, 1267389841, ...

a(35) > 10^5.

Terms > 31 correspond to probable primes.

Examples

			11!4 + 2^8 = 11*7*3*1 + 256 = 487 is prime, so 11 is in the sequence.
		

Links

• Henri & Renaud Lifchitz, PRP Records. Search for n!4+256.
• Joe McLean, Interesting Sources of Probable Primes
• OpenPFGW Project, Primality Tester

Crossrefs

Cf. A007662, A037082, A084438, A123910, A242994.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 4] + 2^8] &]

Extensions

a(34) from Robert Price, Sep 25 2019