OFFSET
1,1
COMMENTS
If it exists, a(6) > 3000. - Jon E. Schoenfield, May 04 2018
If it exists, a(6) > 5703. - J.W.L. (Jan) Eerland, Aug 08 2022
If it exists, a(6) > 10142. - J.W.L. (Jan) Eerland, Aug 14 2022
If it exists, a(6) > 15000. - J.W.L. (Jan) Eerland, Oct 16 2022
If it exists, a(6) > 17506. - J.W.L. (Jan) Eerland, Nov 26 2022
EXAMPLE
5 is in the sequence because 5!-1 reversed is 911, which is prime.
MATHEMATICA
ParallelTable[If[PrimeQ[IntegerReverse[Factorial[k]-1]], k, Nothing], {k, 1, 5703}]//.{}->Nothing (* J.W.L. (Jan) Eerland, Aug 08 2022 *)
PROG
(PARI) isok(n) = isprime(fromdigits(Vecrev(digits(n!-1))));
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Paolo Galliani, May 03 2018
STATUS
approved