A008481 - OEIS

A008481

If n = Product (p_j^k_j) then a(n) = Sum partition(k_j).

0, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 3, 1, 2, 2, 5, 1, 3, 1, 3, 2, 2, 1, 4, 2, 2, 3, 3, 1, 3, 1, 7, 2, 2, 2, 4, 1, 2, 2, 4, 1, 3, 1, 3, 3, 2, 1, 6, 2, 3, 2, 3, 1, 4, 2, 4, 2, 2, 1, 4, 1, 2, 3, 11, 2, 3, 1, 3, 2, 3, 1, 5, 1, 2, 3, 3, 2, 3, 1, 6, 5, 2, 1, 4, 2, 2, 2

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OFFSET

1,4

COMMENTS

a(n) is a function of the prime signature of n (cf. A025487). - Matthew Vandermast, Jun 24 2012

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537 (first 10000 terms from Vincenzo Librandi)

Index entries for sequences computed from exponents in factorization of n.

FORMULA

From Antti Karttunen, Aug 30 2018: (Start)

Additive with a(p^e) = A000041(e).

a(n) = A007814(A318312(n)). (End)

Sum_{k=1..n} a(k) ~ n * (log(log(n)) + B + C), where B is Mertens's constant (A077761) and C = Sum_{p prime} f(1/p) = 1.03089282973521424158..., where f(x) = -1 + (1-x) * Product_{k>=1} (1 + x^k)/(1 - x^(2*k)). - Amiram Eldar, Sep 29 2023

MAPLE

a:= n-> add(combinat[numbpart](i[2]), i=ifactors(n)[2]):

seq(a(n), n=1..100); # Alois P. Heinz, Aug 30 2018

MATHEMATICA

Prepend[ Array[ Plus @@ (PartitionsP /@ Last[ Transpose[ FactorInteger[ # ] ] ])&, 100, 2 ], 0 ]

(* Second program: *)

Array[Total[PartitionsP /@ FactorInteger[#][[All, -1]] - Boole[# == 1]] &, 87] (* Michael De Vlieger, Sep 02 2018 *)

PROG

(PARI) A008481(n) = vecsum(apply(e -> numbpart(e), factor(n)[, 2])); \\ Antti Karttunen, Aug 30 2018

CROSSREFS

Cf. A000041, A007814, A025487, A077761, A318312.

Differs from A318473 for the first time at n=32, where a(32)=7, while A318473(32)=8.

Sequence in context: A069248 A329378 A329617 * A318473 A127669 A323436

Adjacent sequences: A008478 A008479 A008480 * A008482 A008483 A008484

KEYWORD

nonn,easy

AUTHOR

Olivier Gérard

EXTENSIONS

Term a(1) corrected from 1 to 0 (for an empty sum) by Antti Karttunen, Aug 30 2018

STATUS

approved