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 A173099 #4 Jan 03 2022 16:50:49
%S A173099 1,3,2,7,19,240,8861,4244179,75211087198,638418558490509507,
%T A173099 96032307742263928939148386067,
%U A173099 122617614954666266094919182714589930973500782364
%N A173099 a(1)=1, a(2)=3, a(n)=2*a(n-2)*a(n-1)-a(n-2)-a(n-1).
%t A173099 a=1;b=3;lst={a,b};Do[c=2*a*b-a-b;AppendTo[lst,c];a=b;b=c,{n,12}];lst
%t A173099 nxt[{a_,b_}]:={b,2*a*b-a-b}; NestList[nxt,{1,3},12][[All,1]] (* _Harvey P. Dale_, Jan 03 2022 *)
%Y A173099 Cf. A173093, A173094, A173096, A173097, A173098
%K A173099 nonn
%O A173099 1,2
%A A173099 _Vladimir Joseph Stephan Orlovsky_, Feb 09 2010