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A111172 Position of first occurrence of n in A039819. 1
1, 2, 4, 3, 63, 5, 6115, 7, 8, 13, 761401060, 11 (list; graph; refs; listen; history; text; internal format)
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

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Last modified June 12 14:32 EDT 2021. Contains 344957 sequences. (Running on oeis4.)