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A134488 a(0)=1. a(n) = n + d(a(n-1)), where d(m) is the number of positive divisors of m. 1
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, 29, 28, 33, 32, 35, 34, 35, 36, 42, 42, 43, 38, 41, 40, 47, 42, 49, 45, 49, 47, 47, 48, 57, 52, 55, 54, 59, 54, 61, 56, 63, 62, 61, 60, 71, 62, 65, 66, 71, 66, 73, 68, 73, 70, 77, 74 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

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.

LINKS

Table of n, a(n) for n=0..70.

EXAMPLE

a(10)=14 because a(9) (=15) has 4 positive divisors (1,3,5,15) and then a(10)=10+4=14.

MAPLE

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

MATHEMATICA

a = {1}; Do[AppendTo[a, Length[a] + Length[Divisors[a[[ -1]]]]], {70}]; a (* Stefan Steinerberger, Oct 30 2007 *)

CROSSREFS

Cf. A000005.

Sequence in context: A087671 A088308 A167832 * A263800 A168496 A285129

Adjacent sequences:  A134485 A134486 A134487 * A134489 A134490 A134491

KEYWORD

nonn

AUTHOR

Leroy Quet, Oct 28 2007

EXTENSIONS

More terms from Stefan Steinerberger, Oct 30 2007

STATUS

approved

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Last modified July 23 00:43 EDT 2019. Contains 325228 sequences. (Running on oeis4.)