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 A120474 #23 Dec 18 2022 02:33:32
%S A120474 1,-1,1,0,-1,0,1,0,0,-1,1,-1,0,0,1,0,0,0,-1,1,0,-1,1,-1,0,1,-1,0,0,0,
%T A120474 1,0,0,0,0,-1,1,0,0,-1,1,0,-1,1,-1,0,1,0,-1,1,-1,0,1,-1,0,0,1,-1,0,0,
%U A120474 0,0,1,0,0,0,0,0,-1,1,0,0,0,-1,1,0,0,-1,1,0,-1,1,-1,0,1,0,0,-1,1,0,-1,1,-1,0,1,0,-1,1,-1,0,1,-1,0,0,1
%N A120474 Second differences of A004001.
%C A120474 Takes values in {0,1,-1}.
%H A120474 R. J. Mathar, <a href="/A120474/b120474.txt">Table of n, a(n) for n = 1..9998</a>
%F A120474 a(n) = A004001(n+2) - 2*A004001(n+1) + A004001(n) = A093879(n+1) - A093879(n).
%t A120474 Differences[#, 2] &@ Nest[Append[#1, #1[[#1[[-1]] ]] + #1[[#2 - #1[[-1]] ]] ] & @@ {#, Length@ # + 1} &, {1, 1}, 105] (* _Michael De Vlieger_, Nov 05 2018 *)
%Y A120474 Cf. A004001. First differences of A093879.
%K A120474 sign
%O A120474 1,1
%A A120474 _Roger L. Bagula_, Jul 06 2006
%E A120474 Edited by _N. J. A. Sloane_, Oct 01 2006