A363514 Sum of divisors of 3*n-1 of form 3*k+1.

1, 1, 5, 1, 8, 1, 15, 1, 14, 1, 21, 8, 20, 1, 27, 1, 36, 1, 40, 1, 32, 14, 39, 1, 38, 8, 71, 1, 44, 1, 51, 20, 57, 1, 70, 1, 88, 1, 63, 8, 62, 26, 85, 1, 68, 1, 120, 14, 74, 1, 100, 32, 80, 8, 87, 1, 130, 1, 131, 1, 112, 38, 99, 1, 98, 1, 180, 8, 104, 20, 111, 44, 110, 14, 168, 1, 172, 1

Offset

1,3

Links

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

Formula

a(n) = A078181(3*n-1).

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

Mathematica

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

Prog

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

Crossrefs

Cf. A363889, A363890, A363891.

Cf. A078181, A359211.

Sequence in context: A126155 A021197 A286872 * A347955 A349133 A347131

Adjacent sequences: A363511 A363512 A363513 * A363515 A363516 A363517

Keyword

nonn

Author

Seiichi Manyama, Jun 26 2023

Status

approved