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A111291
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Number of refactorable numbers (A033950) <= 10^n.
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0
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1, 4, 16, 92, 665, 5257, 44705, 394240, 3558181, 32608999, 302172507, 2823898245
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Simon Colton conjectures that the number of refactorables less than x is at least x/(2 log(x)).
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LINKS
| S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.
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MATHEMATICA
| c = 0; k = 1; Do[ While[k <= 10^n, If[ Mod[k, DivisorSigma[0, k]] == 0, c++ ]; k++ ]; Print[c], {n, 0, 8}]
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CROSSREFS
| Cf. A033950.
Sequence in context: A139155 A003762 A143501 * A050913 A096243 A131928
Adjacent sequences: A111288 A111289 A111290 * A111292 A111293 A111294
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KEYWORD
| more,nonn
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 01 2005
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EXTENSIONS
| a(9)-a(11) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 19 2009
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