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A072303 Numbers n for which n is congruent to n^2 mod phi(n). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

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

EXAMPLE

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.

PROG

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

CROSSREFS

Cf. A000010, A068494.

Sequence in context: A091897 A055201 A213006 * A242413 A243068 A081061

Adjacent sequences:  A072300 A072301 A072302 * A072304 A072305 A072306

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified April 1 14:39 EDT 2020. Contains 333163 sequences. (Running on oeis4.)