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 A227049 #11 Jul 30 2025 23:33:02 %S A227049 3,31,157,239,1553,5521,25561 %N A227049 Numbers k such that (15^k + 4^k)/19 is prime. %C A227049 All terms are primes. %C A227049 a(8) > 10^5. %t A227049 Select[ Prime[ Range[1, 100000] ], PrimeQ[ (15^# + 4^#)/19 ]& ] %o A227049 (PARI) is(n)=ispseudoprime((15^n+4^n)/19) \\ _Charles R Greathouse IV_, Jun 06 2017 %Y A227049 Cf. A057181, A128071, A128342, A213176, A224501, A221637. %K A227049 hard,nonn,more %O A227049 1,1 %A A227049 _Robert Price_, Jun 29 2013