A174418 Alternately sum and multiply with a(1) = 2 and a(2) = 3.

2, 3, 5, 15, 20, 300, 320, 96000, 96320, 9246720000, 9246816320, 85502721402470400000, 85502721411717216320, 7310715368019097765567999459196928000000

Offset

1,1

Comments

a(n) | a(n+2).

a(n) is approximately c^(2^floor(n/2)) with c = 2.048505746253657024938.... [Charles R Greathouse IV, Nov 07 2011]

Links

Table of n, a(n) for n=1..14.

Formula

a(2n+1) = a(2n) + a(2n-1), a(2n) = a(2n-1) * a(2n-2).

Mathematica

nxt[{n_, a_, b_}]:={n+1, b, If[OddQ[n], a+b, a*b]}; NestList[nxt, {1, 2, 3}, 15][[All, 2]] (* Harvey P. Dale, Feb 26 2020 *)

Prog

(PARI) a=[2, 3]; for(i=1, 9, a=concat(a, [a[#a]+a[#a-1], a[#a]*(a[#a]+a[#a-1])])); a

Crossrefs

Sequence in context: A330988 A102033 A282616 * A072246 A292903 A296051

Adjacent sequences: A174415 A174416 A174417 * A174419 A174420 A174421

Keyword

easy,nonn

Author

Giovanni Teofilatto, Mar 19 2010

Status

approved