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 A228922 #7 Jun 13 2017 14:28:43 %S A228922 5,13,41,43,83,139,557,863,1051,4003 %N A228922 Numbers n such that (19^n + 2^n)/21 is prime. %C A228922 All terms are primes. %C A228922 a(11) > 10^5. %t A228922 Select[Prime[Range[1, 100000]], PrimeQ[(19^# + 2^#)/21]&] %o A228922 (PARI) is(n)=ispseudoprime((19^n+2^n)/21) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A228922 Cf. A057185, A128075, A224507, A225191. %K A228922 nonn,hard,more %O A228922 1,1 %A A228922 _Robert Price_, Sep 08 2013