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Numbers k such that phi(k) == 2 (mod 4).
8

%I #25 Jun 15 2018 21:27:03

%S 3,4,6,7,9,11,14,18,19,22,23,27,31,38,43,46,47,49,54,59,62,67,71,79,

%T 81,83,86,94,98,103,107,118,121,127,131,134,139,142,151,158,162,163,

%U 166,167,179,191,199,206,211,214,223,227,239,242,243,251,254,262,263,271

%N Numbers k such that phi(k) == 2 (mod 4).

%C Related to the equation x^4 = 1 (mod y): sequence gives values of n such x^4 = 1 (mod n) has no solution 1 < x < n-1.

%C k is of the form p^m or 2*p^m where p is A002145 (with the exception of a(2)=4).

%C All prime numbers here belong also to A002145, prime numbers of the form 4n+3. - _Enrique PĂ©rez Herrero_, Sep 07 2011

%D W. J. LeVeque, Fundamentals of Number Theory, pp. 57 Problem 15, Dover NY 1996.

%H Harry J. Smith, <a href="/A066499/b066499.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[300],Mod[EulerPhi[#],4]==2&] (* _Harvey P. Dale_, Feb 18 2018 *)

%o (PARI) { n=0; for (m=1, 10^10, if (eulerphi(m)%4 == 2, write("b066499.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Feb 18 2010

%Y Cf. A066498, A066500, A066501, A066502, A000010.

%Y Essentially the same as A097987.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Jan 04 2002

%E Simpler definition from _Lekraj Beedassy_, Jul 21 2003

%E Corrected and extended by _Ray Chandler_, Nov 06 2003