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 A231374 #6 Jun 13 2017 14:28:47
%S A231374 4,7,19,22,32,46,50,62,83,103,124,142,190,230,256,260,422,596,1084,
%T A231374 2270,2770,5366,5434,5762,6826,9239,15211,22556,58790,81319,172510,
%U A231374 225350,236326,258592,445364,975020
%N A231374 Numbers n such that 3^9*2^n - 1 is prime.
%C A231374 Riesel Primes with k = 3^9 = 19683.
%C A231374 Checked up to n = 1000000.
%e A231374 19683*2^4-1=314927 is a prime number.
%t A231374 i=0;Table[While[i++;cp=19683*2^i-1;!PrimeQ[cp]];i,{j,1,20}]
%o A231374 (PARI) is(n)=ispseudoprime(3^9*2^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A231374 Cf. A002235, A002236, A050539, A050566, A050880, A230527, A230537, A212311.
%K A231374 nonn,hard
%O A231374 1,1
%A A231374 _Lei Zhou_, Nov 08 2013