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 A039771 Numbers k such that phi(k) is a perfect cube. 15
 1, 2, 15, 16, 20, 24, 30, 85, 128, 136, 160, 170, 192, 204, 240, 247, 259, 327, 333, 351, 399, 405, 436, 494, 518, 532, 648, 654, 666, 684, 702, 756, 771, 798, 810, 1024, 1028, 1088, 1111, 1255, 1280, 1360, 1375, 1536, 1542, 1632, 1843, 1853, 1875 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is prime only for a(2)=2, for other cases: eulerphi(p) = p-1 = n^3, and p = 1 + n^3 = (n+1)(n^2-n+1), so p cannot be a prime. - Enrique Pérez Herrero, Aug 29 2010 A013730 is a subsequence. - Enrique Pérez Herrero, Aug 29 2010 LINKS E. Pérez Herrero,Table of n, a(n) for n=1..2500 EXAMPLE phi(247) = 216 = 6*6*6. MATHEMATICA Select[ Range[ 2000 ], IntegerQ[ Power[ EulerPhi[ # ], 1/3 ] ]& ] PROG (PARI) for(n=1, 1e4, if(ispower(eulerphi(n), 3), print1(n", "))) \\ Charles R Greathouse IV, Jul 31 2011 CROSSREFS Cf. A000010, A007614, A216412. Sequence in context: A037312 A267711 A108472 * A032934 A114606 A276114 Adjacent sequences:  A039768 A039769 A039770 * A039772 A039773 A039774 KEYWORD nonn AUTHOR STATUS approved

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Last modified August 17 15:36 EDT 2018. Contains 313816 sequences. (Running on oeis4.)