A363889 Sum of divisors of 3*n-2 of form 3*k+1.

1, 5, 8, 11, 14, 21, 20, 23, 26, 40, 32, 35, 38, 55, 44, 47, 57, 70, 56, 59, 62, 85, 68, 88, 74, 100, 80, 83, 86, 115, 112, 95, 98, 140, 104, 107, 110, 168, 116, 119, 122, 160, 128, 154, 160, 175, 140, 143, 146, 190, 152, 184, 158, 231, 164, 167, 183, 220, 208, 179, 182, 235, 188

Offset

1,2

Links

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

Formula

a(n) = A078181(3*n-2).

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

Mathematica

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

Prog

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

Crossrefs

Cf. A363514, A363890, A363891.

Cf. A078181, A359212.

Sequence in context: A186238 A352623 A314389 * A118520 A001954 A006620

Adjacent sequences: A363886 A363887 A363888 * A363890 A363891 A363892

Keyword

nonn

Author

Seiichi Manyama, Jun 26 2023

Status

approved