A373276 a(n) = Sum_{d|n} (-1)^(d-1) * 3^(n/d-1).

1, 2, 10, 23, 82, 236, 730, 2156, 6571, 19604, 59050, 176918, 531442, 1593596, 4783060, 14346689, 43046722, 129133838, 387420490, 1162241726, 3486785140, 10460294156, 31381059610, 94143003584, 282429536563, 847288078004, 2541865834900, 7625595889958

Offset

1,2

Links

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

Formula

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

If p is an odd prime, a(p) = 1 + 3^(p-1).

Prog

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

Crossrefs

Cf. A048272, A373275.

Cf. A321386, A357051.

Sequence in context: A293403 A316451 A120845 * A330280 A293412 A224837

Adjacent sequences: A373273 A373274 A373275 * A373277 A373278 A373279

Keyword

nonn,easy

Author

Seiichi Manyama, May 29 2024

Status

approved