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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
OFFSET
0,3
COMMENTS
a(n) is even for all n >= 2.
LINKS
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
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