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A067081
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Numbers n such that sigma(n+1)=2*sigma(n).
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5
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5, 125, 1253, 1673, 3127, 5191, 7615, 12035, 43817, 47795, 48559, 49955, 56975, 58373, 61721, 63545, 68033, 78395, 97411, 106001, 108473, 109939, 111451, 111683, 123497, 123797, 131659, 137081, 192065, 192279, 224561, 228377, 274273, 280313
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Sequence seems to give odd values only.
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,761
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MATHEMATICA
| f[n_]:=DivisorSigma[1, n]; lst={}; Do[If[2*f[n]==f[n+1], AppendTo[lst, n]], {n, 9!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Jul 22 2009]
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PROG
| (PARI) { n=0; for (m=1, 10^10, if (sigma(m+1) == 2*sigma(m), write("b067081.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), May 08 2010]
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CROSSREFS
| Sequence in context: A196425 A193612 A195949 * A195801 A154022 A013710
Adjacent sequences: A067078 A067079 A067080 * A067082 A067083 A067084
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KEYWORD
| nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 18 2002
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EXTENSIONS
| Terms added by Harry J. Smith (hjsmithh(AT)sbcglobal.net), May 08 2010
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