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A067130
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Numbers n such that sigma(n-1) divides sigma(n+1).
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3
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2, 34, 55, 119, 285, 367, 835, 849, 919, 1241, 1505, 1559, 2911, 2914, 2939, 3305, 4149, 4188, 6111, 6903, 7170, 7913, 9360, 10251, 10541, 12566, 15086, 17273, 17759, 17815, 19005, 19689, 19919, 21411, 21462, 24882, 25020, 26610, 28125, 30593, 30789, 31485
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Flatten[Position[Partition[DivisorSigma[1, Range[32000]], 3, 1], _?( Divisible[ Last[#], First[#]]&), {1}, Heads->False]]+1 (* Harvey P. Dale, Jan 13 2015 *)
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PROG
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(PARI) isok(n) = sigma(n+1) % sigma(n-1) == 0; \\ Michel Marcus, Nov 20 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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