login
This site is supported by donations to The OEIS Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A129089 a(0)=a(1)=1. a(n) = GCD(a(n-1),n) + GCD(a(n-2),n). 2
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 (list; graph; refs; listen; history; text; internal format)
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: A147848 A239614 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

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 17 10:21 EST 2019. Contains 319218 sequences. (Running on oeis4.)