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A166955
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phi(n) is a perfect power.
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7
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1, 2, 5, 8, 10, 12, 15, 16, 17, 20, 24, 30, 32, 34, 37, 40, 48, 51, 57, 60, 63, 64, 68, 74, 76, 80, 85, 96, 101, 102, 108, 114, 120, 125, 126, 128, 136, 160, 170, 185, 192, 197, 202, 204, 219, 240, 247, 250, 255, 256, 257, 259, 272, 273, 285, 292, 296, 304, 315, 320, 327
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(1)=1 (phi(1)=1^1); a(2)=2 (phi(2)=1^1); a(3)=5 (phi(5)=2^2).
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MATHEMATICA
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ppQ[n_] := GCD @@ Last /@ FactorInteger@ n > 1; ppQ[1] = True; Select[ Range@ 330, ppQ[ EulerPhi[ #]] &] (* Robert G. Wilson v, Dec 12 2012 *)
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PROG
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(PARI) v=[1, 2]; for(n=3, 320, if(ispower(eulerphi(n)), v=concat(v, n))); v (Hobson)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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