A066499 Numbers k such that phi(k) == 2 (mod 4).

3, 4, 6, 7, 9, 11, 14, 18, 19, 22, 23, 27, 31, 38, 43, 46, 47, 49, 54, 59, 62, 67, 71, 79, 81, 83, 86, 94, 98, 103, 107, 118, 121, 127, 131, 134, 139, 142, 151, 158, 162, 163, 166, 167, 179, 191, 199, 206, 211, 214, 223, 227, 239, 242, 243, 251, 254, 262, 263, 271

Offset: 1

Author

Benoit Cloitre, Jan 04 2002

Keywords

• nonn

Comments

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.

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

All prime numbers here belong also to A002145, prime numbers of the form 4n+3. - Enrique Pérez Herrero, Sep 07 2011

References

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

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

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

Essentially the same as A097987.

Cf. A002145.

Programs

Mathematica

Select[Range[300],Mod[EulerPhi[#],4]==2&] (* Harvey P. Dale, Feb 18 2018 *)

PARI

isok(k) = { eulerphi(k)%4 == 2 } \\ Harry J. Smith, Feb 18 2010

Extensions

Simpler definition from Lekraj Beedassy, Jul 21 2003

Corrected and extended by Ray Chandler, Nov 06 2003