OFFSET
1,1
COMMENTS
Corresponding primes are: 2, 3, 23, 401, 8501, 229631, 623641, ...
a(24) > 10^5.
Terms > 29 correspond to probable primes.
LINKS
Henri & Renaud Lifchitz, PRP Records. Search for n!6-4.
Joe McLean, Interesting Sources of Probable Primes
OpenPFGW Project, Primality Tester
EXAMPLE
15!6 - 4 = 15*9*3 - 4 = 401 is prime, so 15 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[4, 50000], PrimeQ[MultiFactorial[#, 6] - 4] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 07 2017
EXTENSIONS
a(22)-a(23) from Robert Price, Aug 03 2018
STATUS
approved