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A099631
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Numbers n such that (sigma(n-2)+sigma(n+2))/2 = sigma(n).
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3
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5, 8, 32, 44, 116, 184, 356, 764, 815, 1004, 1012, 1205, 1338, 1345, 1436, 2636, 2876, 3126, 3644, 5156, 5305, 5804, 6236, 7192, 7542, 7556, 8564, 9356, 9404, 10196, 10362, 10904, 11276, 11876, 13436, 16375, 17564, 17636, 20156, 25316, 25964
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OFFSET
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1,1
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LINKS
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EXAMPLE
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n=5, {n-2,n+2}={3,7}, sigma(3)=4, sigma(7)=8, and sigma(5)=6=(4+8)/2.
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MAPLE
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MATHEMATICA
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Flatten[Position[Partition[DivisorSigma[1, Range[30000]], 5, 1], _?((Last[ #]+ First[ #])/2==#[[3]]&), {1}, Heads->False]]+2 (* Harvey P. Dale, Feb 01 2015 *)
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PROG
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(PARI) isok(n) = (sigma(n-2) + sigma(n+2))/2 == sigma(n); \\ Michel Marcus, Dec 30 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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STATUS
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approved
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