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 A221838 #12 Feb 16 2025 08:33:19 %S A221838 0,0,2,2,2,2,2,6,6,2,2,20,2,2,20,12,2,6,2,20,20,2,2,56,6,2,12,20,2,20, %T A221838 2,20,20,2,20,56,2,2,20,56,2,20,2,20,56,2,2,110,6,6,20,20,2,12,20,56, %U A221838 20,2,2,182,2,2,56,30,20,20,2,20,20,20,2,156,2,2 %N A221838 Number of integer Heron triangles of height n. %H A221838 Eric M. Schmidt, <a href="/A221838/b221838.txt">Table of n, a(n) for n = 1..10000</a> %H A221838 Sourav Sen Gupta, Nirupam Kar, Subhamoy Maitra, Santanu Sarkar, and Pantelimon Stanica, <a href="http://www.emis.de/journals/INTEGERS/papers/n3/n3.Abstract.html">Counting Heron triangles with Constraints</a>, INTEGERS, Electronic J. of Combinatorial Number Theory, Vol. 13, Paper A3, 2013. %H A221838 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HeronianTriangle.html">Heronian Triangle.</a> %F A221838 a(n) = A221837(n) + A046079(n) = A046079(n)^2 + A046079(n). %e A221838 For n = 3, the two triangles have side lengths (3, 4, 5) and (5, 5, 8), with areas 6 and 12 respectively. %o A221838 (Sage) def A221838(n) : pyth = (number_of_divisors(n^2 if n%2==1 else (n/2)^2) - 1) // 2; return pyth^2 + pyth %Y A221838 Cf. A046079, A221837. %K A221838 nonn %O A221838 1,3 %A A221838 _Eric M. Schmidt_, Jan 27 2013