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 A106506 #9 Mar 07 2020 05:08:12
%S A106506 5,7,16,9,11,33,24,13,39,15,56,32,17,51,85,19,72,57,40,95,21,120,105,
%T A106506 23,88,69,48,115,25,161,75,27,104,175,56,135,29,208,189,87,168,145,31,
%U A106506 120,203,93,64,261,155,33,240,217,192,279,165,35,136,231,105,320,72,37,272
%N A106506 Length of side common to the two angles, one being the double of the other, of a primitive integer-sided triangle, sorted on perimeter (A106499).
%F A106506 a(n) = A106501(n)^2 - A106500(n)^2.
%t A106506 sol[p_] := Solve[1 < r < s < 2 r && p == r s + s^2 && GCD[r, s] == 1, {r, s}, Integers];
%t A106506 Reap[For[p = 1, p <= 1000, p++, sp = sol[p]; If[sp =!= {}, Print[s^2 - r^2 /. sp[[1]]]; Sow[s^2 - r^2 /. sp[[1]]]]]][[2, 1]] (* _Jean-François Alcover_, Mar 07 2020 *)
%Y A106506 Cf. A106499-A106505, A106410, A106420, A106430.
%K A106506 nonn
%O A106506 1,1
%A A106506 _Lekraj Beedassy_, May 04 2005
%E A106506 Extended by _Ray Chandler_, May 09 2005