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 A198438 #17 Oct 22 2021 11:33:58
%S A198438 24,120,240,336,840,840,720,1320,2520,2016,3696,2184,5280,5544,6240,
%T A198438 3960,3360,9360,10920,10296,4896,6864,14280,18480,6840,22440,17160,
%U A198438 10920,20064,28560,9240,31824,31920,31416,26520,16320,12144,41496,47880,43680,50160
%N A198438 Common differences in triples of squares in arithmetic progression, that are not a multiples of other triples in (A198384, A198385, A198386).
%H A198438 Ray Chandler, <a href="/A198438/b198438.txt">Table of n, a(n) for n = 1..10000</a>
%H A198438 Keith Conrad, <a href="http://www.math.uconn.edu/~kconrad/blurbs/ugradnumthy/3squarearithprog.pdf">Arithmetic progressions of three squares</a>
%H A198438 Reinhard Zumkeller, <a href="/A198435/a198435.txt">Table of initial values</a>
%F A198438 a(n) = A198387(A198409(n)) = A198436(n) - A198435(n) = A198437(n) - A198436(n).
%t A198438 wmax = 1000;
%t A198438 triples[w_] := Reap[Module[{u, v}, For[u = 1, u < w, u++, If[IntegerQ[v = Sqrt[(u^2 + w^2)/2]], Sow[{u^2, v^2, w^2}]]]]][[2]];
%t A198438 tt = Flatten[DeleteCases[triples /@ Range[wmax], {}], 2];
%t A198438 #[[2]] - #[[1]]& /@ DeleteCases[tt, t_List /; GCD@@t > 1 && MemberQ[tt, t/GCD@@t]] (* _Jean-François Alcover_, Oct 22 2021 *)
%o A198438 (Haskell)
%o A198438 a198438 n = a198438_list !! (n-1)
%o A198438 a198438_list = map a198387 a198409_list
%K A198438 nonn
%O A198438 1,1
%A A198438 _Reinhard Zumkeller_, Oct 25 2011