A119655 - OEIS

%I #17 Jan 20 2018 14:00:49

%S 0,0,2,2,4,2,6,2,8,3,9,2,12,2,12,7,13,2,16,2,16,8,18,2,22,2,23,8,24,2,

%T 27,2,26,11,27,3,32,2,29,14,30,2,38,2,35,14,36,2,42,7,39,16,41,2,46,6,

%U 45,19,43,2,51,2,44,24,46,8,57,2,50,24,55,2,61,2,53,25,55,13,64,2,60

%N a(0) = a(1) = 0. a(n) = number of earlier terms of the sequence which are not coprime to n.

%H Diana L. Mecum, <a href="/A119655/b119655.txt">Table of n, a(n) for n = 0..1199</a>

%e Among the first 20 terms of the sequence there are 8 terms which are not coprime to 21 - a(0)=0, a(1)=0, a(6)=6, a(9)=3, a(10)=9, a(12)=12, a(14)=12 and a(15)=7. So a(21) = 8.

%t a = {0, 0}; Do[AppendTo[a, Length[Select[a, GCD[Length[a], # ] > 1 &]]], {70}]; a (* _Stefan Steinerberger_, Oct 16 2007 *)

%K nonn

%O 0,3

%A _Leroy Quet_, Jul 28 2006

%E More terms from _Stefan Steinerberger_, Oct 16 2007

%E More terms from _Diana L. Mecum_, Aug 15 2008