A111172 Position of first occurrence of n in A039819.

1, 2, 4, 3, 63, 5, 6115, 7, 8, 13, 761401060, 11

Offset

1,2

Comments

The sequence is well-defined because every integer occurs in the sequence A039819 at least once (see S. Colton, Theorem 5). a(11) is probably between 10^8 and 10^9, a(12)=11.

a(14) = 47. a(15) = 170. a(16) = 42. - Donovan Johnson, Apr 04 2011

Links

Table of n, a(n) for n=1..12.

S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.

Example

a(6)=5 because the first 6 occurs in A039819 at position 5.

Mathematica

c = 0; t = Table[0, {100}]; Do[d = DivisorSigma[0, n]; If[ Mod[n, d]==0, c++; If[d < 101 && t[[d]] == 0, t[[d]] = c; Print[{d, c, n}]]], {n, 10^9}]; t (* Robert G. Wilson v *)

Crossrefs

Cf. A039819, A033950.

Sequence in context: A303053 A163089 A258371 * A173556 A247554 A198786

Adjacent sequences: A111169 A111170 A111171 * A111173 A111174 A111175

Keyword

nonn,more

Author

Franz Vrabec, Oct 21 2005

Extensions

a(11) from Donovan Johnson, Apr 04 2011

Status

approved