This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A303937 #45 Dec 16 2024 22:18:17
%S A303937 3,5,19,254,266
%N A303937 Numbers k such that k!-1 reversed is a prime.
%C A303937 If it exists, a(6) > 3000. - _Jon E. Schoenfield_, May 04 2018
%C A303937 If it exists, a(6) > 5703. - _J.W.L. (Jan) Eerland_, Aug 08 2022
%C A303937 If it exists, a(6) > 10142. - _J.W.L. (Jan) Eerland_, Aug 14 2022
%C A303937 If it exists, a(6) > 15000. - _J.W.L. (Jan) Eerland_, Oct 16 2022
%C A303937 If it exists, a(6) > 17506. - _J.W.L. (Jan) Eerland_, Nov 26 2022
%C A303937 If it exists, a(6) > 35000. - _Michael S. Branicky_, Dec 16 2024
%e A303937 5 is in the sequence because 5!-1 reversed is 911, which is prime.
%t A303937 ParallelTable[If[PrimeQ[IntegerReverse[Factorial[k]-1]],k,Nothing],{k,1,5703}]//.{}->Nothing (* _J.W.L. (Jan) Eerland_, Aug 08 2022 *)
%o A303937 (PARI) isok(n) = isprime(fromdigits(Vecrev(digits(n!-1))));
%Y A303937 Cf. A298702, A033312.
%K A303937 nonn,base,more
%O A303937 1,1
%A A303937 _Paolo Galliani_, May 03 2018