A114705 Sum of divisors of 2^n + 3^n.

6, 14, 48, 98, 372, 868, 2784, 7236, 27744, 64708, 215040, 541156, 1947840, 5168548, 23046144, 43129476, 155189760, 444228512, 1398675600, 3623742864, 14636428992, 33799504228, 113272236000, 299806597512, 1154553386688, 2755025768460, 10476271399872, 23113208752200

Offset

1,1

Comments

The terms are never squares. For n>=2, 2^n+3^n falls into a pattern of quadratic non-residues, taken modulo 20: 13, 15, 17, 15, 13, 15, 17, 15, ... - Jack Brennen, Dec 25 2005

a(n) is always even because 2^n+3^n is never a quadratic residue modulo 15. - Jose Brox (tautocrona(AT)terra.es), Dec 27 2005

Links

Amiram Eldar, Table of n, a(n) for n = 1..546

Formula

a(n) = A000203(A007689(n)). - Amiram Eldar, Dec 19 2019

Example

a(3)=48 because 2^3+3^3=8+27=35 has divisors 1,5,7,35 sum of which is 48.

Mathematica

Table[DivisorSigma[1, 2^n+3^n], {n, 1, 30}]

Crossrefs

Cf. A000203, A007689.

Sequence in context: A349835 A294655 A005515 * A200187 A107301 A118432

Adjacent sequences: A114702 A114703 A114704 * A114706 A114707 A114708

Keyword

nonn

Author

Zak Seidov, Dec 26 2005

Extensions

More terms from Amiram Eldar, Dec 19 2019

Status

approved