A359212 Number of divisors of 3*n-2 of form 3*k+1.

1, 2, 2, 2, 2, 3, 2, 2, 2, 4, 2, 2, 2, 4, 2, 2, 3, 4, 2, 2, 2, 4, 2, 4, 2, 4, 2, 2, 2, 4, 4, 2, 2, 5, 2, 2, 2, 6, 2, 2, 2, 4, 2, 4, 4, 4, 2, 2, 2, 4, 2, 4, 2, 6, 2, 2, 3, 4, 4, 2, 2, 4, 2, 4, 2, 6, 2, 2, 2, 6, 2, 2, 4, 6, 2, 2, 2, 4, 2, 4, 2, 4, 4, 4, 2, 5, 4, 2, 2, 4

Offset

1,2

Links

Table of n, a(n) for n=1..90.

Formula

G.f.: Sum_{k>0} x^k/(1 - x^(3*k-2)).

Mathematica

a[n_] := DivisorSum[3*n-2, 1 &, Mod[#, 3] == 1 &]; Array[a, 100] (* Amiram Eldar, Aug 23 2023 *)

Prog

(PARI) a(n) = sumdiv(3*n-2, d, d%3==1);
(PARI) my(N=100, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-x^(3*k-2))))

Crossrefs

Cf. A001817, A359211.

Sequence in context: A033947 A069719 A316990 * A320018 A327162 A326193

Adjacent sequences: A359209 A359210 A359211 * A359213 A359214 A359215

Keyword

nonn,easy

Author

Seiichi Manyama, Dec 21 2022

Status

approved