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A067171
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Numbers k such that sigma(k+1)+sigma(k) = sigma(2k+1).
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4
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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
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OFFSET
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1,2
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COMMENTS
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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
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LINKS
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MATHEMATICA
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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 *)
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PROG
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(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 */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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