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A076648
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phi(n-1) + phi(n+1) = 1/2 sigma(n).
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0
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315, 351, 819, 3375, 24921, 47520, 99540, 107541, 125631, 189175, 410805, 763665, 877365, 1680855, 2480555, 6911079, 7849479, 9646395, 11245365, 12528165, 14242800, 14684055, 16921191, 17194365, 19395025, 27782160, 33830685, 34823075, 36278649, 43955955
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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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phi(314) + phi(316) = 156 + 156 = 312 = 1/2 sigma(315), so 315 belongs to the sequence.
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MATHEMATICA
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Select[Range[2, 10^5], EulerPhi[ # - 1] + EulerPhi[ # + 1] == (1/2)DivisorSigma[1, # ] &]
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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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