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 A160569 #6 Feb 21 2022 12:53:09
%S A160569 1,1,1,-9,-90,-1539,51759,7026831,1349328699,-119669884380,
%T A160569 -462804380329131,-818173230956710191,-775566981773559330471,
%U A160569 23349606875054800260574779,383206716517298992863985977570
%N A160569 a(n)=9*(a(n-1)a(n-3)-a(n-2)^2)/a(n-4), a(1)=a(2)=a(3)=1, a(4)=-9.
%C A160569 a(n+1) is the Hankel transform of A160568.
%H A160569 Harvey P. Dale, <a href="/A160569/b160569.txt">Table of n, a(n) for n = 0..79</a>
%t A160569 nxt[{a_,b_,c_,d_}]:={b,c,d,(9(d*b-c^2))/a}; NestList[nxt,{1,1,1,-9},20][[All,1]] (* _Harvey P. Dale_, Feb 21 2022 *)
%Y A160569 Cf. A050512, A160566.
%K A160569 easy,sign
%O A160569 0,4
%A A160569 _Paul Barry_, May 19 2009