OFFSET
1,2
COMMENTS
The subsequence of primes is A002496 (primes of the form k^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).
MATHEMATICA
Select[Range[1500], SquareFreeQ[#] && IntegerQ @ Sqrt @ EulerPhi[#] &] (* Amiram Eldar, Jul 16 2022 *)
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
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Oct 13 2015
STATUS
approved