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 A243191 #15 Jun 13 2014 11:11:00
%S A243191 0,1,4,7,9,11,13,16,17,25,28,29,36,37,43,44,47,49,52,53,59,63,64,68,
%T A243191 77,81,89,91,97,99,100,107,112,113,116,117,119,121,131,143,144,148,
%U A243191 149,153,163,169,172,175,176,187,188,196,197,199,203,208,211,212,221
%N A243191 Nonnegative integers represented by the indefinite quadratic form x^2+7xy-y^2.
%C A243191 Discriminant 53.
%C A243191 Same as nonnegative integers represented by the form x^2 - 53*y^2 (or 53*x^2 - y^2). - _Robert Israel_, Jun 11 2014
%H A243191 Robert Israel, <a href="/A243191/b243191.txt">Table of n, a(n) for n = 1..10000</a>
%H A243191 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)
%p A243191 select(t -> nops([isolve(x^2-53*y^2=t)])>0, [$0..1000]); # _Robert Israel_, Jun 11 2014
%t A243191 Reap[For[n = 0, n <= 30, n++, If[Reduce[1*x^2 + 7*x*y - 1*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]]
%Y A243191 Cf. A141189 (primes of the form x^2+7*x*y-y^2).
%K A243191 nonn
%O A243191 1,3
%A A243191 _N. J. A. Sloane_, Jun 06 2014
%E A243191 More terms from _Colin Barker_, Jun 10 2014