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 A238240 #15 Oct 22 2024 18:33:27 %S A238240 18,35,50,63,72,74,83,90,95,98,99,107,140,162,171,200,215,227,252,266, %T A238240 275,288,296,315,332,347,359,360,362,371,380,387,392,395,396,407,428, %U A238240 450,491,495,530,539,560,567,602,623,626,635,648,666,684,695,711,722,743,747,755,770,791,794,800,810 %N A238240 Positive integers n such that x^2 - 20xy + y^2 + n = 0 has integer solutions. %C A238240 Positive integers n such that x^2 - 99 y^2 + n = 0 has integer solutions. - _Robert Israel_, Oct 22 2024 %H A238240 Robert Israel, <a href="/A238240/b238240.txt">Table of n, a(n) for n = 1..10000</a> %e A238240 63 is in the sequence because x^2 - 20xy + y^2 + 63 = 0 has integer solutions, for example (x, y) = (1, 16). %p A238240 filter:= t -> [isolve(99*y^2 - z^2 = t)] <> []: %p A238240 select(filter, [$1..1000]); # _Robert Israel_, Oct 22 2024 %Y A238240 Cf. A075839 (n = 18), A221763 (n = 63), A198947 (n = 90), A001085 (n = 99). %Y A238240 Cf. A031363, A084917, A237351, A237599, A237606, A237609, A237610, A236330, A236331. %K A238240 nonn %O A238240 1,1 %A A238240 _Colin Barker_, Feb 20 2014 %E A238240 Corrected by _Robert Israel_, Oct 22 2024