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 A230527 #19 Apr 03 2023 10:36:13
%S A230527 5,17,23,113,125,173,199,319,377,397,785,937,2167,3785,3977,5957,7727,
%T A230527 8249,14677,19577,20485,36319,57509,60703,66677,76877,77017,83407,
%U A230527 229405,1003373
%N A230527 Numbers n such that 3^6*2^n - 1 is prime.
%C A230527 Riesel Primes with k = 3^6 = 729.
%C A230527 Checked up to n = 1003600.
%H A230527 K. Bonath, <a href="http://www.rieselprime.de/">Riesel Prime Database</a>
%H A230527 C. K. Caldwell, <a href="https://t5k.org/primes/page.php?id=72174">729*2^229405-1</a>
%H A230527 C. K. Caldwell, <a href="https://t5k.org/primes/page.php?id=85887">729*2^1003373-1</a>
%e A230527 729*2^5-1=23327 is a prime number.
%t A230527 b=3^6; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 15}]
%o A230527 (PARI) is(n)=ispseudoprime(3^6*2^n-1) \\ _Charles R Greathouse IV_, May 22 2017
%Y A230527 Cf. A002235, A002236, A050539, A050566, A050880.
%K A230527 nonn,hard
%O A230527 1,1
%A A230527 _Lei Zhou_, Oct 22 2013
%E A230527 _Lei Zhou_, Nov 08 2013, added a Mathematica program for small elements.