login
a(1)=1, a(2)=3, a(n)=2*a(n-2)*a(n-1)-a(n-2)-a(n-1).
1

%I #4 Jan 03 2022 16:50:49

%S 1,3,2,7,19,240,8861,4244179,75211087198,638418558490509507,

%T 96032307742263928939148386067,

%U 122617614954666266094919182714589930973500782364

%N a(1)=1, a(2)=3, a(n)=2*a(n-2)*a(n-1)-a(n-2)-a(n-1).

%t 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 nxt[{a_,b_}]:={b,2*a*b-a-b}; NestList[nxt,{1,3},12][[All,1]] (* _Harvey P. Dale_, Jan 03 2022 *)

%Y Cf. A173093, A173094, A173096, A173097, A173098

%K nonn

%O 1,2

%A _Vladimir Joseph Stephan Orlovsky_, Feb 09 2010