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%I #15 Nov 21 2018 04:15:53
%S 1,2,4,6,8,9,9,10,12,15,14,15,16,18,20,21,20,23,20,25,23,23,24,31,26,
%T 29,28,33,32,35,34,35,36,42,42,43,38,41,40,47,42,49,45,49,47,47,48,57,
%U 52,55,54,59,54,61,56,63,62,61,60,71,62,65,66,71,66,73,68,73,70,77,74
%N a(0)=1. a(n) = n + d(a(n-1)), where d(m) is the number of positive divisors of m.
%C Giving the sequence an offset of 1 instead and letting a(1)=1, we get the sequence beginning: 1,3,5,6,9,9,10,12,15,14,15,16,18,20,... This is the same sequence for every term from a(5) on.
%e a(10)=14 because a(9) (=15) has 4 positive divisors (1,3,5,15) and then a(10)=10+4=14.
%p with(numtheory): a[0]:=1: for n to 60 do a[n]:=n+tau(a[n-1]) end do: seq(a[n], n=0..60); # _Emeric Deutsch_, Nov 12 2007
%t a = {1}; Do[AppendTo[a, Length[a] + Length[Divisors[a[[ -1]]]]], {70}]; a (* _Stefan Steinerberger_, Oct 30 2007 *)
%Y Cf. A000005.
%K nonn
%O 0,2
%A _Leroy Quet_, Oct 28 2007
%E More terms from _Stefan Steinerberger_, Oct 30 2007
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