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A166955 phi(n) is a perfect power. 6
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1)=1 (phi(1)=1^1); a(2)=2 (phi(2)=1^1); a(3)=5 (phi(5)=2^2).

MATHEMATICA

ppQ[n_] := GCD @@ Last /@ FactorInteger@ n > 1; ppQ[1] = True; Select[ Range@ 330, ppQ[ EulerPhi[ #]] &] (* Robert G. Wilson v, Dec 12 2012 *)

PROG

(PARI) v=[1, 2]; for(n=3, 320, if(ispower(eulerphi(n)), v=concat(v, n))); v (Hobson)

CROSSREFS

Essentially the same as A065528.

Sequence in context: A237525 A290578 A294127 * A286808 A121294 A039770

Adjacent sequences:  A166952 A166953 A166954 * A166956 A166957 A166958

KEYWORD

nonn,easy

AUTHOR

Juri-Stepan Gerasimov, Oct 25 2009

EXTENSIONS

b-file from Charles R Greathouse IV, Mar 25 2010

STATUS

approved

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Last modified January 20 10:37 EST 2018. Contains 297960 sequences.