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 A128435 a(0)=a(1)=1. For n >= 2, a(n) = number of positive integers which are <= n and are coprime to a(n-1)*a(n-2). 0

%I

%S 1,1,2,2,2,3,2,3,3,6,3,4,4,7,6,4,5,7,13,16,9,7,13,19,22,11,12,8,9,10,

%T 8,13,15,16,9,12,12,13,12,12,13,13,39,27,28,13,18,15,13,25,37,40,20,

%U 22,20,20,22,21,14,17,24,20,17,24,20,17,24,22,21,18,20,19,27,47,49,64,33,23

%N a(0)=a(1)=1. For n >= 2, a(n) = number of positive integers which are <= n and are coprime to a(n-1)*a(n-2).

%e a(7)*a(6) = 6. So a(8) is the number of positive integers which are <= 8 and are coprime to 6. There are 3 such integers (1,5,7), so a(8) = 3.

%p a[0]:=1: a[1]:=1: for n from 2 to 100 do ct:=0: for i from 1 to n do if igcd(i,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 06 2007

%K nonn

%O 0,3

%A _Leroy Quet_, May 05 2007

%E More terms from _Emeric Deutsch_, May 06 2007

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Last modified September 15 20:40 EDT 2019. Contains 327087 sequences. (Running on oeis4.)