1,2

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.

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

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

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 *)

Cf. A039819.

Sequence in context: A053124 A071970 A163089 this_sequence A112793 A009116 A146559

Adjacent sequences: A111169 A111170 A111171 this_sequence A111173 A111174 A111175

nonn

Franz Vrabec (franz.vrabec(AT)aon.at), Oct 21 2005