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A134488
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a(0)=1. a(n) = n + d(a(n-1)), where d(m) is the number of positive divisors of m.
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1
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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; internal format)
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OFFSET
| 0,2
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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 as sequence A134488 for every term from a(5) on.
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EXAMPLE
| a(10)=14 because a(9) (=15) has 4 positive divisors (1,3,5,15) and then a(10)=10+4=14.
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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 (deutsch(AT)duke.poly.edu), Nov 12 2007
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MATHEMATICA
| a = {1}; Do[AppendTo[a, Length[a] + Length[Divisors[a[[ -1]]]]], {70}]; a - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Oct 30 2007
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CROSSREFS
| Sequence in context: A087671 A088308 A167832 * A168496 A160766 A192515
Adjacent sequences: A134485 A134486 A134487 * A134489 A134490 A134491
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Oct 28 2007
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EXTENSIONS
| More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Oct 30 2007
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