A366578 Sum of the divisors of 3^n+1.

3, 7, 18, 56, 126, 434, 1332, 3836, 10476, 42560, 109926, 315112, 816732, 2790074, 8906760, 30220288, 64570086, 229156928, 706911048, 2034690952, 5357742012, 21838961760, 56496274632, 164750562956, 456919958880, 1517043139136, 4661686010664, 16489453890560

Offset: 0

Author

Sean A. Irvine, Oct 13 2023

Keywords

• nonn

Examples

			a(4)=126 because 3^4+1 has divisors {1, 2, 41, 82}.
		

Links

• Max Alekseyev, Table of n, a(n) for n = 0..691

Crossrefs

Cf. A000203, A002592, A024023, A057935, A057941, A074476, A075708, A274909, A366576, A366577, A366579, A366580

Programs

Maple

a:=n->numtheory[sigma](3^n+1):
seq(a(n), n=0..100);

Mathematica

DivisorSigma[1,3^Range[0,30]+1] (* Paolo Xausa, Oct 15 2023 *)

Formula

a(n) = sigma(3^n+1) = A000203(A034472(n)).