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 A050880 #29 Dec 20 2018 14:03:04
%S A050880 2,6,8,11,12,18,24,27,36,38,44,56,58,62,116,134,162,242,274,348,358,
%T A050880 478,512,548,658,824,1242,1287,1531,2846,3343,4818,4856,5051,6024,
%U A050880 7431,7434,9432,9667,13059,13482,18111,19004,33571,40174,41467,53206,57978,61438
%N A050880 Numbers n such that 243*2^n-1 is prime.
%H A050880 Lei Zhou, <a href="/A050880/b050880.txt">Table of n, a(n) for n = 1..67</a>
%H A050880 Ray Ballinger and Wilfrid Keller, <a href="http://www.prothsearch.com/riesel1.html">List of primes k.2^n + 1 for k < 300</a>
%H A050880 Wilfrid Keller, <a href="http://www.prothsearch.com/riesel2.html">List of primes k.2^n - 1 for k < 300</a>
%H A050880 L. Soule and K. Bonath, <a href="http://www.rieselprime.de/">Riesel Prime database</a>
%H A050880 <a href="/index/Pri#riesel">Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime</a>
%t A050880 b=3^5; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 33}] (* _Lei Zhou_, Nov 08 2013 *)
%o A050880 (PARI) is(n)=ispseudoprime(243*2^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017
%K A050880 hard,nonn
%O A050880 1,1
%A A050880 _N. J. A. Sloane_, Dec 29 1999
%E A050880 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008