A357051 a(n) = Sum_{d|n} 3^(n-d).

1, 4, 10, 37, 82, 352, 730, 2998, 7291, 26488, 59050, 263170, 531442, 2127952, 5373460, 19669879, 43046722, 187086916, 387420490, 1607136634, 3878987860, 13947314752, 31381059610, 139902374692, 285916320883, 1129719740248, 2824682785300, 10460357985970

Offset

1,2

Links

Table of n, a(n) for n=1..28.

Formula

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

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

Mathematica

a[n_] := DivisorSum[n, 3^(n-#) &]; Array[a, 28] (* Amiram Eldar, Aug 23 2023 *)

Prog

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

Crossrefs

Cf. A074854, A112329, A359206.

Cf. A342628, A342629, A359203.

Sequence in context: A052572 A079725 A154152 * A370781 A025237 A149188

Adjacent sequences: A357048 A357049 A357050 * A357052 A357053 A357054

Keyword

nonn,easy

Author

Seiichi Manyama, Dec 20 2022

Status

approved