OFFSET
1,2
COMMENTS
a(13) > 10^4.
MAPLE
select(k -> isprime((2*k+1)*k!-1), [$1 .. 300])[];
MATHEMATICA
Do[If[PrimeQ[(2*k + 1)*Factorial[k] - 1], Print[k]], {k, 1, 3000}]
PROG
(PARI) for(k=1, 3000, if(isprime((2*k+1)*k!-1), print1(k", ")))
(SageMath)
for k in range(1, 3000):
if is_prime((2*k+1)*factorial(k) - 1):
print(k)
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Reza K Ghazi, Jun 07 2021
STATUS
approved