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 A051584 #11 Aug 24 2019 11:52:24 %S A051584 0,0,0,0,0,1,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,1,0,0,0,0, %T A051584 0,2,0,0,0,0,0,1,0,0,0,0,0,2,0,0,0,0,0,1,0,0,0,0,0,4,0,0,0,0,0,1,0,0, %U A051584 0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,4,0,0,0,0,0,2,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,1,0,0,0,0,0,4 %N A051584 Number of integer-sided triangles of area n. %C A051584 If integer-sided triangle has integer area, area is divisible by 6. %H A051584 Antti Karttunen, <a href="/A051584/b051584.txt">Table of n, a(n) for n = 1..10085</a> %o A051584 (PARI) %o A051584 A051585(n) = sum(z=sqrtint(sqrtint(192*n^2)-1)+1, sqrtint(9*(64*n^2+5)\20), sum(y=z\2+1, z, my(t=(y*z)^2-(12*n)^2, x); if(issquare(t, &t), (issquare(y^2+z^2-2*t, &x) && x<=y) + (t && issquare(y^2+z^2+2*t, &x) && x<=y), 0))); \\ From A051585 by _Charles R Greathouse IV_ %o A051584 A051584(n) = if((n%6),0,A051585(n/6)); \\ _Antti Karttunen_, Aug 23 2019 %Y A051584 Cf. A051585, A051586. %K A051584 nonn %O A051584 1,12 %A A051584 _David W. Wilson_ %E A051584 Data section extended up to a(120) by _Antti Karttunen_, Aug 23 2019