A359018 a(n) = Sum_{d|n} d * 3^(d-1).

1, 7, 28, 115, 406, 1492, 5104, 17611, 59077, 197242, 649540, 2127364, 6908734, 22325632, 71744968, 229600123, 731794258, 2324583475, 7360989292, 23245426690, 73222477552, 230128420012, 721764371008, 2259438436708, 7060738412431, 22029510754258, 68630377423960

Offset

1,2

Links

Table of n, a(n) for n=1..27.

Formula

G.f.: Sum_{k>=1} x^k/(1 - 3 * x^k)^2.

Mathematica

a[n_] := DivisorSum[n, 3^(#-1)*# &]; Array[a, 27] (* Amiram Eldar, Aug 27 2023 *)

Prog

(PARI) a(n) = sumdiv(n, d, d*3^(d-1));
(PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-3*x^k)^2))

Crossrefs

Cf. A002129, A083413, A359186.

Cf. A034730, A167531, A359189.

Sequence in context: A207098 A037597 A037702 * A302523 A290913 A303406

Adjacent sequences: A359015 A359016 A359017 * A359019 A359020 A359021

Keyword

nonn,easy

Author

Seiichi Manyama, Dec 19 2022

Status

approved