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 A090684 #18 Sep 08 2022 08:45:12
%S A090684 7,31,71,127,199,647,967,1151,1567,2311,2591,2887,3527,4231,4999,5407,
%T A090684 6271,7687,8191,11551,12799,16927,19207,20807,23327,25087,27847,31751,
%U A090684 34847,35911,39199,47431,49927,51199,53791,59167,63367,69191,70687
%N A090684 Primes of the form 8*n^2 - 1.
%C A090684 In the odd number variant of the Ulam spiral, unimpeded by even numbers, prime numbers can line up in horizontal and vertical lines. But there are still noticeable diagonal lines of primes, and these primes fall on one such diagonal.
%H A090684 Vincenzo Librandi, <a href="/A090684/b090684.txt">Table of n, a(n) for n = 1..10000</a>
%t A090684 Select[Table[8n^2 - 1, {n, 9000}], PrimeQ] (* _Alonso del Arte_, Mar 27 2011 *)
%o A090684 (PARI) mx2pmp(n,m) = { for(x=1,n, y = 8*x^2-1; if(isprime(y),print1(y",")) ) }
%o A090684 (Magma) [8*n^2-1: n in [1..95] | IsPrime(8*n^2-1)]; // _Bruno Berselli_, Mar 28 2011
%K A090684 easy,nonn
%O A090684 1,1
%A A090684 _Cino Hilliard_, Dec 18 2003