%I #17 Feb 12 2019 01:16:00

%S 1,1,1,2,3,4,6,3,6,6,3,8,11,13,5,5,6,16,8,7,11,7,7,10,23,15,12,18,7,

%T 24,30,11,32,33,26,35,36,37,38,21,40,41,28,28,19,45,23,23,23,24,49,51,

%U 21,18,33,35,26,57,58,46,28,30,30,17,63,26,66,33,42,37,70,71,47,36,74,28

%N a(0)=a(1)=1. For n >= 2, a(n) = number of positive numbers <= n that are coprime to a(n-1) + a(n-2).

%H Ivan Neretin, <a href="/A128332/b128332.txt">Table of n, a(n) for n = 0..10000</a>

%e a(5) + a(6) = 10. The number of positive integers <= 7 that are coprime to 10 is three, these integers being 1, 3 and 7. So a(7) = 3.

%p a[0]:=1: a[1]:=1: for n from 2 to 100 do ct:=0: for j from 1 to n do if igcd(j,a[n-1]+a[n-2])=1 then ct:=ct+1 else fi od: a[n]:=ct: od: seq(a[n],n=0..100); # _Emeric Deutsch_, May 07 2007

%t nxt[{n_,a_,b_}]:={n+1,b,Count[Range[n+1],_?(CoprimeQ[a+b,#]&)]}; Transpose[ NestList[ nxt,{1,1,1},80]][[2]] (* _Harvey P. Dale_, Jan 21 2015 *)

%Y Cf. A000010 (number of positive numbers <= n that are coprime to n).

%K nonn

%O 0,4

%A _Leroy Quet_, May 04 2007

%E More terms from _Emeric Deutsch_, May 07 2007