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 A224931 #14 Apr 28 2013 15:41:58 %S A224931 0,0,0,1,1,0,2,1,2,2,3,3,4,3,4,6,6,4,7,5,6,9,8,9,10,9,9,9,15,9,15,12, %T A224931 11,15,13,12,20,18,16,15,21,17,21,18,20,21,25,20,22,23,25,24,27,22,29, %U A224931 26,28,31,34,26,35,32,26,33,35,30,41,33,36,34,42,35 %N A224931 Number of integer parallelograms with integer side lengths n = a >= b and integer diagonal lengths e >= f. %C A224931 It is easy to see that a < e < a + b and e^2 + f^2 = 2(a^2 + b^2). %H A224931 Reiner Moewald, <a href="/A224931/b224931.txt">Table of n, a(n) for n = 1..200</a> %Y A224931 Cf. A224932, A224933. %K A224931 nonn %O A224931 1,7 %A A224931 _Reiner Moewald_, Apr 20 2013