A129089 a(0)=a(1)=1. a(n) = gcd(a(n-1), n) + gcd(a(n-2), n).

1, 1, 2, 2, 4, 2, 4, 2, 6, 4, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 6, 4, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 10, 2, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 6, 4, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 10, 2, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 6, 4, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 10, 2, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2, 6, 4, 4, 2, 6, 2, 4, 2, 6, 2, 8, 2

Offset

0,3

Comments

a(n) is even for all n >= 2.

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Maple

a[0]:=1: a[1]:=1: for n from 2 to 130 do a[n]:=igcd(a[n-1], n)+igcd(a[n-2], n) od: seq(a[n], n=0..130); # Emeric Deutsch, Apr 16 2007

Mathematica

nxt[{n_, a_, b_}]:={n+1, b, GCD[b, n+1]+GCD[a, n+1]}; Join[{1}, NestList[nxt, {1, 1, 1}, 110][[All, 3]]] (* Harvey P. Dale, May 23 2017 *)

Crossrefs

Cf. A129088.

Sequence in context: A239614 A358216 A193432 * A255201 A169594 A294337

Adjacent sequences: A129086 A129087 A129088 * A129090 A129091 A129092

Keyword

nonn

Author

Leroy Quet, Mar 29 2007

Extensions

More terms from Emeric Deutsch, Apr 16 2007

Incorrect g.f. removed by Georg Fischer, May 15 2019

Status

approved