OFFSET
1,1
COMMENTS
Corresponding primes are 38557, 189757, 17961239276317, 3091650738156317, ... .
a(31) > 50000.
LINKS
Henri & Renaud Lifchitz, PRP Records. Search for n!3-19683.
Joe McLean, Interesting Sources of Probable Primes
EXAMPLE
16!3 - 3^9 = 16*13*10*7*4*1 - 19683 = 58240 - 19683 = 38557 is prime, so 16 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
Select[Range[15, 50000], PrimeQ[MultiFactorial[#, 3] - 3^9] &]
Select[Range[12, 33100], PrimeQ[Times@@Range[#, 1, -3]-19683]&] (* Harvey P. Dale, Jan 25 2021 *)
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Robert Price, Jan 09 2016
STATUS
approved