The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A124071 a(1)=1. a(n) = GCD(n,a(n-1)) + GCD(n+1,a(n-1)). 0

%I

%S 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,

%T 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,

%U 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

%N a(1)=1. a(n) = GCD(n,a(n-1)) + GCD(n+1,a(n-1)).

%C 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

%p 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

%t 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_ *)

%K nonn

%O 1,2

%A _Leroy Quet_, Nov 05 2006

%E More terms from _Emeric Deutsch_ and _Robert G. Wilson v_, Nov 06 2006

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 December 9 07:21 EST 2021. Contains 349627 sequences. (Running on oeis4.)