A085149 Numbers k such that k!!!!! - 1 is prime.

3, 4, 6, 7, 8, 12, 13, 14, 27, 28, 33, 35, 44, 50, 62, 64, 74, 88, 114, 140, 142, 242, 248, 262, 270, 284, 395, 473, 582, 600, 634, 707, 805, 882, 907, 1008, 1152, 1243, 1853, 2340, 2410, 2703, 2793, 3033, 3600, 3925, 4124, 4154, 6185, 6367, 7130, 9104, 9992

Offset: 1

Author

Hugo Pfoertner, Jun 23 2003

Keywords

• hard
• nonn

Comments

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

• Robert Price, Table of n, a(n) for n = 1..63
• Ken Davis, Status of Search for Multifactorial Primes.
• Ken Davis, Results for n!5-1.

Crossrefs

Cf. A085157 (quintuple factorials), A085148.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 1000], PrimeQ[MultiFactorial[#, 5] - 1] & ] (* Robert Price, Apr 19 2019 *)

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

a(54)-a(63) from Ken Davis link added to b-file by Robert Price, Sep 23 2012