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 A228076 #22 Mar 07 2021 02:12:59 %S A228076 2,7,11,31,47,139,263,769,20551,21491,112247 %N A228076 Numbers k such that (19^k - 4^k)/15 is prime. %C A228076 All terms are prime. %C A228076 a(12) > 2*10^5. %t A228076 Select[Prime[Range[1, 100000]], PrimeQ[(19^# - 4^#)/15]&] %o A228076 (PARI) is(n)=ispseudoprime((19^n-4^n)/15) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A228076 Cf. A224691, A128354, A128032. %K A228076 nonn,hard,more %O A228076 1,1 %A A228076 _Robert Price_, Aug 09 2013 %E A228076 a(11) from _Robert Price_, Mar 06 2021