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A111291 Number of refactorable numbers (A033950) <= 10^n. +0
1
1, 4, 16, 92, 665, 5257, 44705, 394240, 3558181 (list; graph; listen)
OFFSET

0,2

COMMENT

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: A009568 A139155 A003762 this_sequence A050913 A096243 A131928

Adjacent sequences: A111288 A111289 A111290 this_sequence A111292 A111293 A111294

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 01 2005

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Last modified August 29 17:54 EDT 2008. Contains 143238 sequences.


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