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A275245
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Numbers n such that phi(n) divides n^2 while phi(n) does not divide n.
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0
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10, 20, 40, 42, 50, 60, 80, 84, 100, 114, 120, 126, 136, 156, 160, 168, 180, 200, 220, 228, 240, 250, 252, 272, 294, 300, 312, 320, 336, 342, 360, 378, 400, 440, 444, 456, 468, 480, 500, 504, 540, 544, 588, 600, 624, 640, 672, 684, 720, 756, 800, 816
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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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10 is a term because phi(10) = 4; 10 mod 4 = 2 and 10^2 mod 4 = 0.
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MATHEMATICA
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Select[Range[10^3], Function[k, And[Divisible[#^2, k], ! Divisible[#, k]]]@ EulerPhi@ # &] (* Michael De Vlieger, Jul 21 2016 *)
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PROG
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(PARI) isok(n) = (n % eulerphi(n) != 0) && (n^2 % eulerphi(n) == 0)
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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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