OFFSET
1,1
COMMENTS
n=5 and n=8 produce values (-6551 and -6481) whose absolute value is a prime.
Corresponding primes are: 51679, 202879, 4182239, 608601439, 2504895839, ...
a(40) > 50000.
Terms > 26 correspond to probable primes.
LINKS
Henri & Renaud Lifchitz, PRP Records. Search for n!3-6561.
Joe McLean, Interesting Sources of Probable Primes
OpenPFGW Project, Primality Tester
EXAMPLE
16!3 - 3^8 = 16*13*10*7*4*1 - 6561 = 51679 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[0, 50000], PrimeQ[MultiFactorial[#, 3] - 3^8] &]
Select[Range[14, 800], PrimeQ[Times@@Range[#, 1, -3]-6561]&] (* The program generates the first 21 terms of the sequence. To generate more, increase the Range constant. *) (* Harvey P. Dale, Apr 27 2022 *)
PROG
(PARI) for(n=1, 1e3, if(ispseudoprime(prod(i=0, floor((n-1)/3), n-3*i) - 3^8), print1(n, ", "))) \\ Altug Alkan, Nov 18 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Nov 18 2015
STATUS
approved