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A345029 a(n) = Sum_{k=1..n} 3^(floor(n/k) - 1). 3
1, 4, 11, 32, 87, 258, 745, 2224, 6605, 19784, 59151, 177438, 531733, 1595104, 4783811, 14351228, 43049043, 129147030, 387427357, 1162281532, 3486804959, 10460413130, 31381119537, 94143358500, 282429716209, 847289143468, 2541866366735, 7625599086782 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..2000

FORMULA

G.f.: (1/(1 - x)) * Sum_{k>=1} x^k * (1 - x^k)/(1 - 3*x^k).

MATHEMATICA

a[n_] := Sum[3^(Floor[n/k] - 1), {k, 1, n}]; Array[a, 30] (* Amiram Eldar, Jun 06 2021 *)

PROG

(PARI) a(n) = sum(k=1, n, 3^(n\k-1));

(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, x^k*(1-x^k)/(1-3*x^k))/(1-x))

CROSSREFS

Column k=3 of A345032.

Cf. A003462, A345035.

Sequence in context: A027153 A319918 A034754 * A268744 A038747 A052545

Adjacent sequences:  A345026 A345027 A345028 * A345030 A345031 A345032

KEYWORD

nonn

AUTHOR

Seiichi Manyama, Jun 06 2021

STATUS

approved

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Last modified January 16 13:05 EST 2022. Contains 350376 sequences. (Running on oeis4.)