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A111291
Number of refactorable numbers (A033950) <= 10^n.
0
1, 4, 16, 92, 665, 5257, 44705, 394240, 3558181, 32608999, 302172507, 2823898245
OFFSET
0,2
COMMENTS
Simon Colton conjectures that the number of refactorables less than x is at least x/(2 log(x)).
LINKS
S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.
MATHEMATICA
c = 0; k = 1; Do[ While[k <= 10^n, If[ Mod[k, DivisorSigma[0, k]] == 0, c++ ]; k++ ]; Print[c], {n, 0, 8}]
CROSSREFS
Cf. A033950.
Sequence in context: A139155 A003762 A143501 * A050913 A096243 A263565
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Nov 01 2005
EXTENSIONS
a(9)-a(11) from Donovan Johnson, Sep 19 2009
STATUS
approved