A247939 Sum of divisors of 2^prime(n)+1.

6, 13, 48, 176, 2736, 10928, 174768, 699056, 11184816, 727960800, 2863311536, 183355069408, 2967356682528, 11728124029616, 188313058624992, 12121838249371488, 768906329487027264, 3074457345618258608, 196765296972010592800, 3148244377723715041632

Offset: 1

Author

Vincenzo Librandi, Sep 27 2014

Keywords

• nonn

Comments

b-file computed with factorizations in Wagstaff link. a(166) corresponding to 2^983+1 is currently the first unknown term. - Jens Kruse Andersen, Sep 28 2014

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..165
• Sam Wagstaff, The Cunningham Project

Crossrefs

Cf. A000203, A069061, A098640.

Programs

Magma

[SumOfDivisors(2^p+1): p in PrimesUpTo(100)];

Maple

with(numtheory): A247939:=n->sigma(2^ithprime(n)+1): seq(A247939(n), n=1..20); # Wesley Ivan Hurt, Sep 27 2014

Mathematica

Table[DivisorSigma[1, 2^Prime[n] + 1], {n, 1, 20}]

PARI

vector(50,n,sigma(2^prime(n)+1)) \\ Derek Orr, Sep 27 2014

Formula

a(n) = A000203(A098640(n)). - Michel Marcus, Sep 27 2014