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A126132 a(n) = number of k's, 1<=k<=n, where d(k) is equal to any divisor of n, where d(k) is the number of positive divisors of k. 1

%I

%S 1,2,1,3,1,5,1,7,3,5,1,12,1,7,3,12,1,12,1,15,3,9,1,23,2,10,4,19,1,19,

%T 1,23,4,12,2,33,1,13,4,31,1,22,1,29,6,15,1,45,1,18,5,32,1,31,2,40,5,

%U 17,1,53,1,19,6,45,2,33,1,41,5,23,1,69,1,22,6,45,2,39,1,59,6,23,1,70,3,24,5

%N a(n) = number of k's, 1<=k<=n, where d(k) is equal to any divisor of n, where d(k) is the number of positive divisors of k.

%e The number of divisors of the integers 1 through 10 form the sequence 1,2,2,3,2, 4,2,4,3,4. The divisors of 10 are 1,2,5,10. The terms of the sequence of the first ten d(k)'s which equal any divisor of 10 are the five terms 1,2,2,2,2. So a(10) = 5.

%t f[n_] := Length@Select[Table[Length@Divisors[k], {k, n}], MemberQ[Divisors[n], # ] &];Table[f[n], {n, 87}] (* _Ray Chandler_, Dec 20 2006 *)

%Y Cf. A126131.

%K nonn

%O 1,2

%A _Leroy Quet_, Dec 18 2006

%E Extended by _Ray Chandler_, Dec 20 2006

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Last modified February 26 18:29 EST 2020. Contains 332293 sequences. (Running on oeis4.)