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URL: https://oeis.org/A072989

⇱ A072989 - OEIS

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A072989
Numbers m>0 such that the number of solutions to x^m==1 (mod m), 1<=x<=m, is not equal to gcd(m, phi(m)).
4
20, 30, 40, 42, 52, 60, 66, 68, 70, 78, 80, 84, 90, 100, 102, 104, 110, 114, 116, 120, 126, 130, 132, 136, 138, 140, 148, 150, 154, 156, 160, 164, 168, 170, 171, 174, 180, 182, 186, 190, 198, 200, 204, 208, 210, 212, 220, 222, 228, 230, 232, 234, 238, 240
OFFSET
1,1
COMMENTS
Conjecture: limit of a(n)/n is zero.
This conjecture is certainly wrong as stated, because sequences "Numbers such that..." have lim a(n)/n >= 1 and a(n) > n for all indices following the first one for which this holds, as here: a(1) > 1. - M. F. Hasler, Feb 24 2014
LINKS
FORMULA
Equals { m>0 | A009195(m) != A072994(m) }. - M. F. Hasler, Feb 23 2014
PROG
(PARI) isok(m) = sum(x=1, m, Mod(x, m)^m==1) != gcd(m, eulerphi(m)); \\ Michel Marcus, Feb 18 2021
CROSSREFS
Sequence in context: A029721 A224400 A132067 * A216603 A166730 A109944
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Aug 21 2002
STATUS
approved