A072303 Numbers n for which n is congruent to n^2 mod phi(n).

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 16, 17, 18, 19, 21, 23, 24, 25, 27, 28, 29, 31, 32, 36, 37, 41, 43, 47, 48, 49, 53, 54, 59, 61, 64, 67, 71, 72, 73, 79, 81, 83, 89, 96, 97, 101, 103, 107, 108, 109, 112, 113, 121, 125, 127, 128, 131, 137, 139, 144, 149, 151, 157

Offset: 1

Author

Igor Naverniouk (igor(AT)lexansoft.com), Jul 14 2002

Keywords

• easy
• nonn

Comments

Or, numbers n such that phi(n) divides n*(n-1). - Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 14 2006

Examples

			9 is in the sequence because phi(9) = 6. 9 % 6 = 3 and 9^2 % 6 = 3. But 10 is not in the sequence because phi(10) = 4 and 10 % 4 = 6 and 10^2 % 4 = 0.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A068494.

Programs

PARI

isok(n) = ((n^2 - n) % eulerphi(n)) == 0 \\ Michel Marcus, Jun 07 2013