1,2

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

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

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.

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

Cf. A000010, A068494.

Sequence in context: A091897 A055201 A213006 * A242413 A243068 A081061

Adjacent sequences: A072300 A072301 A072302 * A072304 A072305 A072306

easy,nonn

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

approved