A112646 Special solutions to abs(sigma(x+1) - sigma(x)) = 2 where x + 1 = 3^y.

8, 26, 2186, 1594322, 7509466514979724803946715958257546, 13915193059764305937984450503671774362956903094026

Offset: 1

Author

Labos Elemer, Sep 28 2005

Keywords

• nonn

Comments

The relevant computed exponents providing -1+3^z solutions for A112645 are 2, 3, 7, 13, 71, 103.

The next term, if it exists, is too large to include here. - N. J. A. Sloane, Jul 12 2009

Contribution from David Wasserman, Jul 06 2009: No more terms < 10^86.

Crossrefs

Cf. A000203, A112645, A112647.

Programs

Mathematica

ta={{0}};Do[s=Abs[DivisorSigma[1, 3^n]-DivisorSigma[1, -1+3^n]]; If[Equal[s, 2], ta=Append[ta, n];Print[ -1+3^n]], {n, 1, 100000000}]; ta=Delete[ta, 1]