A051592 Numbers k such that k!!!!!! - 1 is prime.

3, 4, 6, 12, 14, 54, 74, 102, 114, 302, 318, 366, 614, 1178, 1188, 3110, 7284, 21432, 21906, 25848, 29882, 38618, 41990, 84510, 86022

Offset: 1

Author

N. J. A. Sloane

Keywords

• hard
• nonn

Comments

k!!!!!! = k*(k-6)*(k-12)*(k-18)*...

The search for multifactorial primes started by Ray Ballinger is now continued by a team of volunteers on the website of Ken Davis (see link).

Links

• Ray Ballinger, Status of Search for Multifactorial Primes.
• Ken Davis, Status of Search for Multifactorial Primes.
• Ken Davis, Results for n!6-1..

Crossrefs

Cf. A085158 (sextuple factorials), A085150.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 1000], PrimeQ[MultiFactorial[#, 6] - 1] & ] (* Robert Price, Apr 19 2019 *)

Extensions

Edited and extended by Hugo Pfoertner, Jun 23 2003

Corrected and extended by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008