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%I #9 Sep 16 2015 00:43:57
%S 1,1,2,2,2,5,2,2,2,9,2,11,2,13,14,3,3,16,3,18,18,18,6,18,8,19,8,21,9,
%T 29,9,9,25,26,26,26,12,26,26,26,16,41,16,29,30,31,17,33,18,33,33,33,
%U 22,33,33,33,33,33,28,58,30,34,34,33,34,63,36,34,34
%N a(1) = 1. For n >= 2, a(n) = number of earlier terms of the sequence which are divisible by a different number of distinct primes than n.
%e Among the 15 earliest terms of the sequence there are 3 terms not divisible by exactly one distinct prime, as 16 is. (These 3 terms are 1, 1 {both divisible by 0 primes} and 14 {divisible by 2 distinct primes}.) So a(16) = 3.
%t a = {1}; For[n = 2, n < 70, n++, c = 0; For[j = 1, j < Length[a] + 1, j++, If[Not[Length[FactorInteger[a[[j]]]] == Length[FactorInteger[n]]], c++ ]]; AppendTo[a, c]]; a (* _Stefan Steinerberger_, Nov 21 2007 *)
%Y Cf. A001221.
%K nonn
%O 1,3
%A _Leroy Quet_, Dec 28 2005
%E More terms from _Stefan Steinerberger_, Nov 21 2007
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