A363890 Sum of divisors of 3*n-1 of form 3*k+2.

2, 5, 10, 11, 16, 17, 27, 23, 28, 29, 42, 40, 40, 41, 57, 47, 57, 53, 80, 59, 64, 70, 87, 71, 76, 88, 115, 83, 88, 89, 117, 100, 114, 101, 140, 107, 128, 113, 147, 136, 124, 130, 170, 131, 136, 137, 216, 154, 148, 149, 200, 160, 160, 184, 207, 167, 194, 173, 241, 179, 224, 190, 237

Offset

1,1

Links

Seiichi Manyama, Table of n, a(n) for n = 1..10000

Formula

a(n) = A078182(3*n-1).

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

Mathematica

a[n_] := DivisorSum[3*n - 1, # &, Mod[#, 3] == 2 &]; Array[a, 100] (* Amiram Eldar, Jun 26 2023 *)

Prog

(PARI) a(n) = sumdiv(3*n-1, d, (d%3==2)*d);

Crossrefs

Cf. A363514, A363889, A363891.

Cf. A078182, A359211.

Sequence in context: A230408 A163624 A353356 * A257031 A167799 A179871

Adjacent sequences: A363887 A363888 A363889 * A363891 A363892 A363893

Keyword

nonn

Author

Seiichi Manyama, Jun 26 2023

Status

approved