id:A068594 - OEIS Search Results

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Factorable subsets: the number of subsets S of {1,2,...,n} that can be expressed in the form S=A*B, where B is defined to be the set {a(i)*b(j)| a(i) in A, b(j) in B}.

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0, 0, 0, 3, 3, 11, 11, 23, 33, 63, 63, 137, 137, 257, 320 (list; graph; listen)

	OFFSET	`1,4`
	EXAMPLE	`a(6)=11, since {4}={2}{2}, {2,4}={2}{1,2}, {6}={2}{3}, {2,6}={2}{1,3}, {4,6}={2}{2,3}, {2,4,6}={2}{1,2,3}, {1,2,4}={1,2}{1,2}, {3,6}={1,2}{3}, {1,2,3,6}={1,2}{1,3}, {2,3,4,6}={1,2}{2,3}, {1,2,3,4,6}={1,2}*{1,2,3}, and no other subsets of {1,2,...,6} can be so factored.`
	CROSSREFS	`Sequence in context: A107229 A122167 A095019 this_sequence A122573 A136123 A045495` `Adjacent sequences: A068591 A068592 A068593 this_sequence A068595 A068596 A068597`
	KEYWORD	`nonn`
	AUTHOR	`John W. Layman (layman(AT)math.vt.edu), Mar 14 2002`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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