cp's OEIS Frontend

A335689 Denominator of b(n), where b(1)=b(2)=1, and for n>2, b(n) = (1+b(n-2))/b(n-1).

%I A335689 #14 Sep 20 2023 19:55:35
%S A335689 1,1,1,1,1,3,1,18,5,2268,575,673840944,787879375,
%T A335689 135166424574775691397888,419139972928839518312890625,
%U A335689 3664804294228230129440232448667132628447640073019295936217088,23745903429826252844483444331595197466499151820665748466452878317718505859375
%N A335689 Denominator of b(n), where b(1)=b(2)=1, and for n>2, b(n) = (1+b(n-2))/b(n-1).
%C A335689 With a tiny change in subscripts {b(n)} becomes the Lyness 5-cycle, a sequence of period 5, as illustrated in A076839.
%e A335689 1, 1, 2, 1, 3, 2/3, 6, 5/18, 126/5, 115/2268, 297108/575, 1370225/673840944, 200590993732752/787879375, ...
%t A335689 nxt[{a_,b_}]:={b,(1+a)/b}; NestList[nxt,{1,1},20][[;;,1]]//Denominator (* _Harvey P. Dale_, Sep 20 2023 *)
%Y A335689 Cf. A076839, A335688.
%K A335689 nonn,frac
%O A335689 1,6
%A A335689 _N. J. A. Sloane_, Jul 17 2020