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 A050566 #21 Jan 17 2019 10:08:17
%S A050566 3,5,11,17,21,27,81,101,107,327,383,387,941,1665,3515,4007,4727,7137,
%T A050566 16257,16833,21243,24239,35435,59925,91673,153455,165341,183167,
%U A050566 190349,240743,253385,308325,741917
%N A050566 Numbers n such that 81*2^n-1 is prime.
%H A050566 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 A050566 Wilfrid Keller, <a href="http://www.prothsearch.com/riesel2.html">List of primes k.2^n - 1 for k < 300</a>
%H A050566 <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>
%H A050566 Kosmaj, <a href="http://www.15k.org/riesellist.html">Riesel list k<300</a>.
%t A050566 b=81; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 17}]
%o A050566 (PARI) is(n)=ispseudoprime(81*2^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017
%K A050566 hard,nonn
%O A050566 1,1
%A A050566 _N. J. A. Sloane_, Dec 29 1999
%E A050566 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A050566 _Lei Zhou_, Nov 08 2013, added a Mathematica program for small elements.