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 A121459 #21 Feb 15 2020 03:45:41
%S A121459 0,-3,-14,-18,-7,-9,-47,-51,0,-15,-15,-48,-17,-36,57,-151,0,-63,0,-11,
%T A121459 0,25,26,368,29,-5,-96,-33,0,-144,2275,-466,-180,433,472,0,-43,316,0,
%U A121459 0,47,-302,49,152,1122,945,1273,10170,589,1310,121,54,3117,0,177,2141,-1280,-5,310,0
%N A121459 Let f(n) = A004001(n)^2 - A005185(n)^2. Then a(n) = f(abs(f(n-1))) + f(abs(n - f(n-1))).
%H A121459 G. C. Greubel, <a href="/A121459/b121459.txt">Table of n, a(n) for n = 1..350</a>
%t A121459 HConway[n_]:= HConway[n]= If[n<3, 1, HConway[HConway[n-1]] + HConway[n-HConway[n -1]]];
%t A121459 Hofstadter[n_]:= Hofstadter[n]= If[n<3, 1, Hofstadter[n -Hofstadter[n-1]] + Hofstadter[n -Hofstadter[n-2]]];
%t A121459 f[n_]:= f[n]= HConway[n]^2 - Hofstadter[n]^2;
%t A121459 Table[f[Abs[f[n-1]]] + f[Abs[n -f[n-1]]], {n,60}] (* corrected by _G. C. Greubel_, Feb 12 2020 *)
%Y A121459 Cf. A004001, A005185.
%K A121459 sign,less
%O A121459 1,2
%A A121459 _Roger L. Bagula_, Sep 06 2006
%E A121459 Edited by _N. J. A. Sloane_, Oct 01 2006
%E A121459 Terms a(31) and beyond corrected by _G. C. Greubel_, Feb 12 2020