A124071 a(1)=1. a(n) = GCD(n,a(n-1)) + GCD(n+1,a(n-1)).

1, 2, 3, 2, 3, 4, 5, 2, 3, 2, 3, 4, 3, 4, 5, 2, 3, 4, 5, 6, 5, 2, 3, 4, 3, 4, 5, 2, 3, 4, 5, 2, 3, 2, 3, 4, 3, 4, 5, 6, 7, 8, 5, 6, 5, 2, 3, 4, 3, 4, 5, 2, 3, 4, 5, 2, 3, 2, 3, 4, 3, 4, 5, 6, 7, 2, 3, 4, 3, 2, 3, 4, 3, 4, 5, 2, 3, 4, 5, 6, 5, 2, 3, 4, 3, 4, 5, 2, 3, 4, 5, 2, 3, 2, 3, 4, 3, 4, 5, 6, 7, 2, 3, 4, 3

Offset

1,2

Comments

First occurrence of k: 1, 2, 3, 6, 7, 20, 41, 42, 127, 1304, 1809, 2530, 2531, 42132, 113413, 113414, 196575, 3160096, 3160097, 3160098, 3160099, 3160100, 3160101, ..., . - Robert G. Wilson v, Nov 07 2006

Links

Table of n, a(n) for n=1..105.

Maple

a[1]:=1: for n from 2 to 130 do a[n]:=gcd(n, a[n-1])+gcd(n+1, a[n-1]) od: seq(a[n], n=1..130); # Emeric Deutsch, Nov 06 2006

Mathematica

a[1] = 1; a[n_] := a[n] = GCD[n, a[n - 1]] + GCD[n + 1, a[n - 1]]; Array[a, 105] (* Robert G. Wilson v *)

Crossrefs

Sequence in context: A070770 A292599 A071487 * A034697 A110157 A178493

Adjacent sequences: A124068 A124069 A124070 * A124072 A124073 A124074

Keyword

nonn

Author

Leroy Quet, Nov 05 2006

Extensions

More terms from Emeric Deutsch and Robert G. Wilson v, Nov 06 2006

Status

approved