A126870 - OEIS

%I #11 Oct 30 2019 17:33:16

%S 1,1,2,2,4,5,6,3,6,9,10,9,12,7,7,8,16,15,18,17,8,21,22,20,20,12,16,17,

%T 28,10,30,12,9,33,7,28,36,17,16,33,40,9,42,43,19,37,46,39,41,42,21,24,

%U 52,45,25,32,24,57,58,23,60,34,24,28,15,29,66,65,29,27,70,57,72,39,35

%N a(1)=1. a(n) = number of earlier terms of the sequence which are coprime to the sum of distinct prime divisors of n.

%e The sum of the distinct prime divisors of 12 is 2+3 = 5. So a(12) is the number of terms from among (a(1),a(2),...a(11)) which are coprime to 5. There are 9 such terms, so a(12) = 9.

%t g[l_List] := Block[{n = Length[l] + 1},Append[l, Count[GCD[l, f[n]], 1]]];Nest[g, {1}, 75] (* _Ray Chandler_, Mar 26 2007 *)

%Y Cf. A008472.

%K nonn

%O 1,3

%A _Leroy Quet_, Mar 16 2007

%E Extended by _Ray Chandler_, Mar 26 2007