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 A205521 #19 Aug 31 2017 04:13:36
%S A205521 1,3,7,13,25,243,349,3645,10245,40647,40749
%N A205521 Numbers n such that 4*11^n - 1 is prime.
%t A205521 Table[If[PrimeQ[4*11^n-1],Print[n];n],{n,1,20000}]
%o A205521 (PARI) is(n)=ispseudoprime(4*11^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A205521 Cf. A199020 (4*11^n-1).
%Y A205521 Cf. A120378 (numbers n such that 2*11^n - 1 is prime).
%Y A205521 Cf. A046865 (numbers n such that 4*5^n - 1 is prime).
%Y A205521 Cf. A005540 (numbers n such that 4*3^n - 1 is prime).
%K A205521 nonn
%O A205521 1,2
%A A205521 _José María Grau Ribas_, Jan 28 2012
%E A205521 a(10)-a(11) from _Dmitry Khomovsky_, Aug 30 2017