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 A128000 #20 Dec 12 2017 01:47:54 %S A128000 2,5,17,457,1423,115877 %N A128000 Numbers n such that (28^n - 1)/27 is prime. %C A128000 No other terms less than 100000. - _Robert Price_, May 01 2012 %H A128000 H. 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 A128000 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %H A128000 <a href="/index/Pri#primepop">Index to primes in various ranges</a>, form ((k+1)^n-1)/k %t A128000 Select[Prime[Range[100]],PrimeQ[(28^#-1)/27]&] %o A128000 (PARI) is(n)=ispseudoprime((28^n-1)/27) \\ _Charles R Greathouse IV_, Jun 13 2017 %K A128000 hard,more,nonn %O A128000 1,1 %A A128000 _Alexander Adamchuk_, Feb 11 2007 %E A128000 1423 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008 %E A128000 a(6)=115877 corresponds to a probable prime discovered by _Paul Bourdelais_, Dec 08 2017