A067171 Numbers k such that sigma(k+1)+sigma(k) = sigma(2k+1).

1, 4, 646, 1096, 16174, 22891, 64672, 353110, 468970, 515698, 733570, 1317343, 1633213, 1735288, 2026945, 2093506, 2709542, 4413772, 5005825, 5346241, 5388154, 6134527, 12811666, 15453229, 19063174, 20565214, 22172791, 35476021

Offset

1,2

Comments

Integer solutions x to (q=sigma[x]+sigma[x+1])/sigma[x+x+1] such that q=1, i.e., sigma[x]+sigma[x+1])=sigma[2x+1]; sigma[]=A000203. - Labos Elemer, Feb 16 2004

Links

Donovan Johnson, Table of n, a(n) for n = 1..100

Mathematica

Do[s=(DivisorSigma[1, n]+DivisorSigma[1, n+1])/ DivisorSigma[1, 2*n+1]; If[Equal[s, 1], Print[n]], {n, 1, 10000000}] (* Labos Elemer, Feb 16 2004 *)

Prog

(PARI) s1=1; for(n=1, 10^9, s2=sigma(n+1); if(s1+s2==sigma(2*n+1), print1(n, ", ")); s1=s2) /* Donovan Johnson, Sep 17 2013 */

Crossrefs

Cf. A000203, A091287, A091289, A091290.

Sequence in context: A169619 A337650 A091288 * A046348 A332164 A334528

Adjacent sequences: A067168 A067169 A067170 * A067172 A067173 A067174

Keyword

nonn

Author

Benoit Cloitre, Feb 18 2002

Extensions

More terms from Labos Elemer, Feb 16 2004

Edited by N. J. A. Sloane, Oct 02 2008 at the suggestion of R. J. Mathar

a(22)-a(28) from Donovan Johnson, Jan 31 2009

Status

approved