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 A123702 #10 Oct 11 2019 12:31:41
%S A123702 1,1,-1,-2,3,4,18,408,175824,30989858688,960376803619751958528,
%T A123702 922323604960653729254933704147036248735744,
%U A123702 850680832267616036448642743307003648114050501920269009809993262836200003241653567488
%N A123702 a(1)=a(2)=1. For n >= 3, a(n) = (product{k=1 to n-1} a(k)) - (sum{j=1 to n-1} a(j)).
%C A123702 a(3) and a(4) are the only negative terms of the sequence.
%F A123702 For n >= 5, a(n) = a(n-1) a(n-2) (a(n-1)-1) /(a(n-2)-1).
%t A123702 f[l_List] := Append[l, Times @@ l - Plus @@ l];Nest[f, {1, 1}, 11] (* _Ray Chandler_, Oct 09 2006 *)
%Y A123702 Cf. A123703.
%K A123702 easy,sign
%O A123702 1,4
%A A123702 _Leroy Quet_, Oct 08 2006
%E A123702 Extended by _Ray Chandler_, Oct 09 2006