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

8, 26, 2186, 1594322, 7509466514979724803946715958257546, 13915193059764305937984450503671774362956903094026

Offset

1,1

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.

Links

Table of n, a(n) for n=1..6.

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]

Crossrefs

Cf. A000203, A112645, A112647.

Sequence in context: A000810 A171740 A129663 * A119522 A070494 A334659

Adjacent sequences: A112643 A112644 A112645 * A112647 A112648 A112649

Keyword

nonn

Author

Labos Elemer, Sep 28 2005

Status

approved