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 A028951 #21 Jul 08 2025 18:57:28
%S A028951 0,1,2,4,7,8,9,11,14,16,18,22,23,25,28,29,32,36,37,43,44,46,49,50,53,
%T A028951 56,58,63,64,67,71,72,74,77,79,81,86,88,92,98,99,100,106,107,109,112,
%U A028951 113,116,121,126,127,128,134,137,142,144,148,149,151,154,158,161,162
%N A028951 Numbers represented by quadratic form with Gram matrix [ 2, 1; 1, 4 ] (or the Kleinian 2-d lattice, see A002652).
%C A028951 Or, numbers of the form x^2+xy+2y^2 with x and y integers. - _N. J. A. Sloane_, Apr 30 2015
%H A028951 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 A028951 Reap[For[n = 0, n < 200, n++, r = Reduce[x^2 + x y + 2 y^2 == n, {x, y}, Integers]; If[r =!= False, Sow[n]]]][[2, 1]] (* _Jean-François Alcover_, Oct 31 2016 *)
%Y A028951 Cf. A028929, A035248, A002652, A034036, A257346 (complement).
%K A028951 nonn
%O A028951 1,3
%A A028951 _N. J. A. Sloane_
%E A028951 More terms from Larry Reeves (larryr(AT)acm.org), Mar 29 2000