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 A106420 #11 Mar 07 2020 05:07:56
%S A106420 6,12,15,20,30,28,35,42,40,56,45,63,72,70,66,90,77,88,99,84,110,91,
%T A106420 104,132,117,130,143,126,156,120,154,182,165,144,195,176,210,153,170,
%U A106420 208,187,204,240,221,198,238,255,190,234,272,209,228,247,220,266,306,285
%N A106420 Length of side opposite the greater of the two angles, one being the double of the other, of a primitive integer-sided triangle, sorted on perimeter (A106499).
%F A106420 a(n) = A106500(n) * A106501(n).
%t A106420 sol[p_] := Solve[1 < r < s < 2 r && p == r s + s^2 && GCD[r, s] == 1, {r, s}, Integers];
%t A106420 Reap[For[p = 1, p <= 1000, p++, sp = sol[p]; If[sp =!= {}, Print[r s /. sp[[1]]]; Sow[r s /. sp[[1]]]]]][[2, 1]] (* _Jean-François Alcover_, Mar 07 2020 *)
%Y A106420 Cf. A106499-A106506, A106410, A106430.
%K A106420 nonn
%O A106420 1,1
%A A106420 _Lekraj Beedassy_ and _Ray Chandler_, May 09 2005