A111291 Number of refactorable numbers (A033950) <= 10^n.

1, 4, 16, 92, 665, 5257, 44705, 394240, 3558181, 32608999, 302172507, 2823898245

Offset: 0

Author

Robert G. Wilson v, Nov 01 2005

Keywords

• more
• nonn

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.

Crossrefs

Cf. A033950.

Programs

Mathematica

c = 0; k = 1; Do[ While[k <= 10^n, If[ Mod[k, DivisorSigma[0, k]] == 0, c++ ]; k++ ]; Print[c], {n, 0, 8}]

Extensions

a(9)-a(11) from Donovan Johnson, Sep 19 2009