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 A181987 #13 Jun 13 2017 13:46:16 %S A181987 349,631,4493,16633,36341 %N A181987 Numbers n such that (39^n - 1)/38 is prime. %H A181987 Harvey Dubner, <a href="http://dx.doi.org/10.1090/S0025-5718-1993-1185243-9">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927-930. %H A181987 Henri Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %t A181987 Select[Prime[Range[100000]], PrimeQ[(39^#-1)/38]&] %o A181987 (PARI) is(n)=ispseudoprime((39^n-1)/38) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A181987 Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127995, A127996, A127997, A127998, A127999, A098438, A128002, A128003, A128004, A128005. %K A181987 hard,more,nonn %O A181987 1,1 %A A181987 _Robert Price_, Apr 04 2012