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 A028955 #19 Jul 08 2025 18:57:56 %S A028955 0,2,3,5,8,12,17,18,20,23,27,30,32,38,45,47,48,50,53,57,62,68,72,75, %T A028955 80,83,92,93,95,98,102,107,108,113,120,122,125,128,137,138,147,152, %U A028955 153,155,158,162,167,170,173,180,183,188,192,197,200,207,212,218,227,228 %N A028955 Numbers represented by quadratic form with Gram matrix [ 4, 1; 1, 4 ] (divided by 2). %C A028955 Numbers of the form 2*x^2 + x*y + 2*y^2, of discriminant -15. - _N. J. A. Sloane_, Jun 01 2014 %C A028955 8*a(n) is of the form z^2 + 15*y^2, where z = 4*x + y. [_Bruno Berselli_, Jul 12 2014] %H A028955 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) %F A028955 a(x, y) = (4x^2 + 2xy + 4y^2)/2; x, y any integer. %e A028955 32 is in the sequence because it can be written in the form 2*2^2+2*3+2*3^2, and hence 8*32 = 11^2+15*3^2. %Y A028955 Cf. A028927. For primes see A106859. %K A028955 nonn,easy %O A028955 1,2 %A A028955 _N. J. A. Sloane_ %E A028955 More terms from Larry Reeves (larryr(AT)acm.org), Mar 29 2000