A366666 Sum of the divisors of 9^n+1.

3, 18, 126, 1332, 10476, 109926, 816732, 8906760, 64570086, 706911048, 5357742012, 56496274632, 456919958880, 4661686010664, 35152280388792, 388532214509688, 2779530283277766, 30018958465575240, 230668806145962744, 2431533550553980488, 19410628990783168944

Offset: 0

Author

Sean A. Irvine, Oct 15 2023

Keywords

• nonn

Examples

			a(2)=126 because 9^2+1 has divisors {1, 2, 41, 82}.
		

Links

• Max Alekseyev, Table of n, a(n) for n = 0..345

Crossrefs

Cf. A062396, A000203, A057935, A366662, A366664, A366665, A366667.

Cf. A069061, A366578, A366607, A366617, A366629, A366638, A366657, A366668, A366689, A366715.

Programs

Maple

a:=n->numtheory[sigma](9^n+1):
seq(a(n), n=0..100);

Mathematica

DivisorSigma[1, 9^Range[0,20] + 1] (* Paul F. Marrero Romero, Nov 14 2023 *)

Formula

a(n) = sigma(9^n+1) = A000203(A062396(n)).

a(n) = A366578(2*n). - Max Alekseyev, Jan 08 2024