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A072079 Sum of 3-smooth divisors of n. 2
1, 3, 4, 7, 1, 12, 1, 15, 13, 3, 1, 28, 1, 3, 4, 31, 1, 39, 1, 7, 4, 3, 1, 60, 1, 3, 40, 7, 1, 12, 1, 63, 4, 3, 1, 91, 1, 3, 4, 15, 1, 12, 1, 7, 13, 3, 1, 124, 1, 3, 4, 7, 1, 120, 1, 15, 4, 3, 1, 28, 1, 3, 13, 127, 1, 12, 1, 7, 4, 3, 1, 195, 1, 3, 4, 7, 1, 12, 1, 31, 121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = A000203(A065331(n)).

Multiplicative with a(2^e) = 2^(e+1)-1, a(3^e) = (3^(e+1)-1)/2, a(p^e) = 1, p>3. Christian G. Bower May 20, 2005.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = (2^(A007814(n)+1)-1)*(3^(A007949(n)+1)-1)/2.

MATHEMATICA

f[p_, e_] := If[p > 3, 1, (p^(e + 1) - 1)/(p - 1)]; a[1] = 1; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Aug 29 2019 *)

CROSSREFS

Cf. A000203, A003586, A072078.

Sequence in context: A322017 A093087 A130893 * A116073 A166043 A294896

Adjacent sequences:  A072076 A072077 A072078 * A072080 A072081 A072082

KEYWORD

nonn,mult

AUTHOR

Reinhard Zumkeller, Jun 13 2002

STATUS

approved

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Last modified April 11 03:12 EDT 2021. Contains 342886 sequences. (Running on oeis4.)