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%I #6 Mar 16 2015 10:10:52
%S 0,1,3,7,15,37,75,167,359,785,1571,3447,6895,14367,29783,61303,122607,
%T 250783,501567,1018031,2053407,4127231,8254463,16610879,33311679,
%U 66737871,133719583,267778623,535557247,1072160511,2144321023,4291006911,8584417343,17171483103,34348627135,68706410943
%N Number of repeating products of any subset of {1, 2, 3, ..., n}.
%F a(n) = 2^n - 1 - A060957(n) = A000225(n) - A060957(n).
%e a(3) = (number of possible subsets of {1,2,3}) - |{1, 2, 3, 1*2, 1*3, 2*3, 1*2*3}| = 2^3-1 - |{1,2,3,6}| = 3. Equivalently, there are three repeating products (2, 3, and 6) so a(3) = 3.
%t (* Script not convenient for n > 24 *) f[n_] := Block[{lst = Times @@@ Subsets[Range@ n, n]}, 2^n - 1 - Length@ Select[Tally@ lst, Last@ # > 1 &]]; Array[f, 16] (* _Michael De Vlieger_, Mar 13 2015 *)
%Y Cf. A000225, A060957.
%K nonn
%O 1,3
%A _Derek Orr_, Mar 11 2015
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