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 A224691 #7 Jun 13 2017 10:30:45 %S A224691 2,5,19,109,157,8521,26017,26177 %N A224691 Numbers n such that (13^n - 4^n)/9 is prime. %C A224691 All terms are prime. %C A224691 a(9) > 10^5. %t A224691 Select[Prime[Range[1, 100000]], PrimeQ[(13^# - 4^#)/9]&] %o A224691 (PARI) is(n)=ispseudoprime((13^n-4^n)/9) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A224691 Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032, A210506, A128347. %K A224691 nonn,hard,more %O A224691 1,1 %A A224691 _Robert Price_, Apr 15 2013