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 A156686 #8 Feb 04 2020 13:30:44
%S A156686 2,4,4,6,6,6,8,8,8,10,10,10,12,12,12,12,12,12,14,14,14,16,16,16,16,18,
%T A156686 18,18,18,18,20,20,20,20,20,20,22,22,22,24,24,24,24,24,24,24,24,24,26,
%U A156686 26,26,28,28,28,28,28,28,30,30,30,30,30,30,30,30,30
%N A156686 The ordered set of a + b - c as (a,b,c) runs through all Pythagorean triples with a<b<c.
%C A156686 Also called the excess of a Pythagorean triangle, and is equal to the diameter of its incircle. All members of this sequence are even, and the corresponding sequence for primitive triangles only is A020887.
%H A156686 Ray Chandler, <a href="/A156686/b156686.txt">Table of n, a(n) for n = 1..10000</a>
%H A156686 Darryl McCullough, <a href="http://www.math.ou.edu/~dmccullough/teaching/pythagoras2.pdf">Height and Excess of Pythagorean Triples</a>
%H A156686 Darryl McCullough, <a href="http://www.jstor.org/stable/3219271">Height and Excess of Pythagorean Triples</a>, Mathematics Magazine, Vol. 78, No. 1, February 2005.
%e A156686 The smallest excess in any Pythagorean triangle is 2, which occurs in (3,4,5) because 3+4-5=2. Hence a(1)=2.
%t A156686 data1=Reduce[ a^2+b^2==c^2 && a+b-c==# && 0<a<b<c,{a,b,c},Integers]&/@Range[30];DeleteCases[Table[If[Head[data1[[k]]]===Symbol,0,If[Head[data1[[k]]]===And,k,Table[k,{i,1,Length[data1[[k]]]}]]],{k,1,Length[data1]}],0]//Flatten
%Y A156686 Cf. A020887.
%K A156686 easy,nice,nonn
%O A156686 1,1
%A A156686 _Ant King_, Feb 18 2009