A366638 Sum of the divisors of 7^n+1.

3, 15, 93, 660, 3606, 34560, 236964, 1559520, 9155916, 77423280, 530807472, 3868683120, 21224771760, 185094572580, 1261494915594, 9988783073280, 49990612274316, 436182213726030, 3279858902194056, 21372989348391720, 122709716651985624, 1082323574100172800

Offset: 0

Author

Sean A. Irvine, Oct 15 2023

Keywords

• nonn

Examples

			a(4)=3606 because 7^4+1 has divisors {1, 2, 1201, 2402}.
		

Links

• Max Alekseyev, Table of n, a(n) for n = 0..387

Crossrefs

Cf. A034491, A000203, A057937, A227575, A366634, A366636, A366637, A366639.

Cf. A069061, A366578, A366607, A366617, A366629, A366657, A366666, A366668, A366689, A366715.

Programs

Maple

a:=n->numtheory[sigma](7^n+1):
seq(a(n), n=0..100);

Mathematica

DivisorSigma[1, 7^Range[0, 21] + 1] (* Paul F. Marrero Romero, Oct 16 2023 *)

Formula

a(n) = sigma(7^n+1) = A000203(A034491(n)).