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

1, 1, 1, 1, 1, 3, 1, 18, 5, 2268, 575, 673840944, 787879375, 135166424574775691397888, 419139972928839518312890625, 3664804294228230129440232448667132628447640073019295936217088, 23745903429826252844483444331595197466499151820665748466452878317718505859375

Offset

1,6

Comments

With a tiny change in subscripts {b(n)} becomes the Lyness 5-cycle, a sequence of period 5, as illustrated in A076839.

Links

Table of n, a(n) for n=1..17.

Example

1, 1, 2, 1, 3, 2/3, 6, 5/18, 126/5, 115/2268, 297108/575, 1370225/673840944, 200590993732752/787879375, ...

Mathematica

nxt[{a_, b_}]:={b, (1+a)/b}; NestList[nxt, {1, 1}, 20][[;; , 1]]//Denominator (* Harvey P. Dale, Sep 20 2023 *)

Crossrefs

Cf. A076839, A335688.

Sequence in context: A346039 A143849 A370233 * A105626 A071210 A051141

Adjacent sequences: A335686 A335687 A335688 * A335690 A335691 A335692

Keyword

nonn,frac

Author

N. J. A. Sloane, Jul 17 2020

Status

approved