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 A212311 #16 Apr 03 2023 10:36:13
%S A212311 1,15,33,43,61,121,295,315,367,681,771,789,1485,4915,5305,33649,81343,
%T A212311 85005,116307,154869,230731,279591,287847,329515,545353,1053481
%N A212311 Numbers n such that 3^8*2^n - 1 is prime.
%C A212311 Riesel Primes with k = 3^8 = 6561.
%C A212311 Checked up to n = 1053627.
%H A212311 K. Bonath,<a href="http://www.rieselprime.de/">Riesel Prime Database</a>
%H A212311 C. K. Caldwell, <a href="https://t5k.org/primes/page.php?id=103608">6561*2^1053481-1</a>
%e A212311 6561*2^1-1=13121 is a prime number.
%t A212311 b=2^8;i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 13}]
%o A212311 (PARI) is(n)=ispseudoprime(3^8*2^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A212311 Cf. A002235, A002236, A050539, A050566, A050880, A230527, A230537.
%K A212311 nonn,hard
%O A212311 1,2
%A A212311 _Lei Zhou_, Oct 24 2013
%E A212311 _Lei Zhou_, Nov 08 2013, added a Mathematica program for small elements.