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 A262406 Squarefree n such that phi(n) is a perfect square. 3
 1, 2, 5, 10, 17, 34, 37, 57, 74, 85, 101, 114, 170, 185, 197, 202, 219, 257, 273, 285, 370, 394, 401, 438, 451, 489, 505, 514, 546, 570, 577, 629, 677, 679, 802, 902, 969, 978, 985, 1010, 1057, 1095, 1154, 1258, 1285, 1297, 1354, 1358, 1365 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The subsequence of primes is A002496: the primes of form n^2+1. - Michel Marcus, Oct 14 2015 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 W. D. Banks, J. B. Friedlander, C. Pomerance and I. E. Shparlinski, Multiplicative structure of values of the Euler function, in High Primes and Misdemeanours: Lectures in Honour of the Sixtieth Birthday of Hugh Cowie Williams (A. Van der Poorten, ed.), Fields Inst. Comm. 41 (2004), pp. 29-47. FORMULA Banks, Friedlander, Pomerance, and Shparlinski show that a(n) = O(n^1.421). PROG (PARI) is(n)=my(f=factor(n)); issquare(eulerphi(f)) && (n==1 || vecmax(f[, 2])==1) (MAGMA) [n: n in [1..1400] | IsSquarefree(n) and IsSquare(EulerPhi(n))]; // Vincenzo Librandi, May 05 2016 CROSSREFS Intersection of A039770 and A005117. Cf. A000010, A007614, A068560, A004171, A114063. Sequence in context: A038358 A107482 A227363 * A018315 A146220 A054964 Adjacent sequences:  A262403 A262404 A262405 * A262407 A262408 A262409 KEYWORD nonn AUTHOR Charles R Greathouse IV, Oct 13 2015 STATUS approved

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Last modified August 18 13:28 EDT 2018. Contains 313832 sequences. (Running on oeis4.)