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A116009
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Numbers k such that k + sigma(k) + phi(k) is a square.
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3
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3, 81, 400, 972, 1209, 1276, 1480, 1833, 2700, 3408, 4080, 4345, 6321, 6498, 6885, 8673, 8697, 10257, 12325, 13192, 13240, 13409, 14496, 14560, 16932, 17232, 18168, 18904, 19140, 19344, 20196, 22896, 23568, 23920, 27001, 27313, 28305
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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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81 + sigma(81) + phi(81) = 16^2.
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MATHEMATICA
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Select[Range[30000], IntegerQ@Sqrt[# +DivisorSigma[1, #]+EulerPhi[#]] &] (* Amiram Eldar, Aug 13 2019 *)
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PROG
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(PARI) isok(n) = issquare (n + sigma(n) + eulerphi(n)); \\ Michel Marcus, Jan 26 2014
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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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