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 A237609 #14 Jan 09 2015 08:56:44 %S A237609 7,13,17,19,28,41,52,61,63,68,73,76,77,83,101,112,117,131,139,143,153, %T A237609 161,164,167,171,173,175,187,208,209,227,241,244,252,259,271,272,283, %U A237609 292,293,299,304,307,308,325,332,343,349,369,371,391,404,409,425,437 %N A237609 Positive integers k such that x^2 - 9xy + y^2 + k = 0 has integer solutions. %e A237609 7 is in the sequence because x^2 - 9xy + y^2 + 7 = 0 has integer solutions, for example (x, y) = (1, 8). %o A237609 (PARI) is(n)=bnfisintnorm(bnfinit(x^2-9*x+1),-n) \\ _Ralf Stephan_, Feb 11 2014 %Y A237609 Cf. A070998 (k = 7). %Y A237609 Cf. A031363, A084917, A237351, A237599, A237606, A237610. %K A237609 nonn %O A237609 1,1 %A A237609 _Colin Barker_, Feb 10 2014