This site is supported by donations to The OEIS Foundation.

 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: A306652 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 Incorrect g.f. removed by Georg Fischer, May 15 2019 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.

Last modified October 14 14:22 EDT 2019. Contains 328017 sequences. (Running on oeis4.)