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A055574
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n satisfying sigma(n+1) = sigma(n-1).
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13
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34, 55, 285, 367, 835, 849, 919, 1241, 1505, 2911, 2914, 3305, 4149, 4188, 6111, 6903, 7170, 7913, 9360, 10251, 10541, 12566, 15086, 17273, 17815, 19005, 19689, 21411, 21462, 24882, 25020, 26610, 28125, 30593, 30789, 31485, 38211, 38983
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OFFSET
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1,1
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COMMENTS
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Numbers n such that antisigma(n+1) - antisigma(n-1) = 2*n + 1, where antisigma(m) = A024816(m) = sum of nondivisors of m. - Jaroslav Krizek, Mar 17 2013
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LINKS
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EXAMPLE
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sigma(34-1) = 48 = sigma(34+1), so 34 is a term of the sequence.
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MATHEMATICA
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Select[Range[10^5], DivisorSigma[1, # + 1] == DivisorSigma[1, # - 1] &]
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PROG
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(PARI) x=y=1; forfactored(z=3, 10^6, if(sigma(z)==sigma(x), print1(y[1]", ")); x=y; y=z) \\ Charles R Greathouse IV, May 09 2017
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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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