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 A139501 #4 Jun 19 2014 15:28:19
%S A139501 23,47,73,101,131,139,163,197,233,239,271,277,311,347,349,353,397,443,
%T A139501 461,463,491,499,541,577,587,593,647,653,691,719,739,761,809,821,823,
%U A139501 853,859,883,929,947,967,997,1013,1051,1061,1087,1151,1163,1223,1277
%N A139501 Primes of the form x^2 + 21x*y + y^2 for x and y nonnegative.
%H A139501 N. J. A. Sloane et al., <a href="https://oeis.org/wiki/Binary_Quadratic_Forms_and_OEIS">Binary Quadratic Forms and OEIS</a> (Index to related sequences, programs, references)
%t A139501 a = {}; w = 21; k = 1; Do[Do[If[PrimeQ[n^2 + w*n*m + k*m^2], AppendTo[a, n^2 + w*n*m + k*m^2]], {n, m, 400}], {m, 1, 400}]; Union[a] (*Artur Jasinski*)
%Y A139501 Cf. A139489, A007645, A068228, A007519, A033212, A033212, A107152, A107008, A033215, A107145, A139490, A139491.
%K A139501 nonn
%O A139501 1,1
%A A139501 _Artur Jasinski_, Apr 24 2008