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A067171
Numbers k such that sigma(k+1)+sigma(k) = sigma(2k+1).
4
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
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
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