OFFSET
1,2
COMMENTS
It's obvious that 1 is the only number k such that k!+k is prime.
There is no further term up to 5000.
There is no further term up to 25000. - Michael S. Branicky, Nov 14 2024
EXAMPLE
37!+37 = 13763753091226345046315979581580902400000037 and reversal(37!+37) =
73000000420908518597951364054362219035736731 is prime, so 37 is in the sequence.
MATHEMATICA
reversal[n_]:=FromDigits[Reverse[IntegerDigits[n]]];
Do[If[PrimeQ[reversal[n!+n]], Print[n]], {n, 5000}]
CROSSREFS
KEYWORD
base,hard,more,nonn,changed
AUTHOR
Farideh Firoozbakht, Oct 22 2009
STATUS
approved