|
%I #13 May 03 2015 03:37:27
%S 1,2,4,3,63,5,6115,7,8,13,761401060,11
%N Position of first occurrence of n in A039819.
%C 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.
%C a(14) = 47. a(15) = 170. a(16) = 42. - _Donovan Johnson_, Apr 04 2011
%H S. Colton, <a href="http://www.cs.uwaterloo.ca/journals/JIS/colton/joisol.html">Refactorable Numbers - A Machine Invention</a>, J. Integer Sequences, Vol. 2, 1999, #2.
%e a(6)=5 because the first 6 occurs in A039819 at position 5.
%t 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_ *)
%Y Cf. A039819, A033950.
%K nonn,more
%O 1,2
%A _Franz Vrabec_, Oct 21 2005
%E a(11) from _Donovan Johnson_, Apr 04 2011
|
