A366576 Sum of the divisors of 3^n-1.

3, 15, 42, 186, 399, 1680, 3282, 15876, 31836, 123690, 277344, 1541568, 2391486, 8992680, 25483332, 111757968, 193819392, 967814400, 1744488660, 9366647892, 16912999320, 62424587520, 144219337920, 852903426816, 1397135488896, 4766016364260, 12477973754400

Offset: 1

Author

Sean A. Irvine, Oct 13 2023

Keywords

• nonn

Examples

			a(4)=186 because 3^4-1 has divisors {1, 2, 4, 5, 8, 10, 16, 20, 40, 80}.
		

Links

• Max Alekseyev, Table of n, a(n) for n = 1..690

Crossrefs

Cf. A024023, A000203, A075708, A133801, A295500, A366575.

Cf. A075708, A366603, A366613, A366622, A366634, A366653, A366662, A102146, A366684, A366710.

Programs

Maple

a:=n->numtheory[sigma](3^n-1):
seq(a(n), n=1..100);

Mathematica

DivisorSigma[1,3^Range[30]-1] (* Paolo Xausa, Oct 15 2023 *)

Formula

a(n) = sigma(3^n-1) = A000203(A024023).