

A109606


Number of numbers k with 1 < k < n which are relatively prime to n.


7



0, 0, 1, 1, 3, 1, 5, 3, 5, 3, 9, 3, 11, 5, 7, 7, 15, 5, 17, 7, 11, 9, 21, 7, 19, 11, 17, 11, 27, 7, 29, 15, 19, 15, 23, 11, 35, 17, 23, 15, 39, 11, 41, 19, 23, 21, 45, 15, 41, 19, 31, 23, 51, 17, 39, 23, 35, 27, 57, 15, 59, 29, 35, 31, 47, 19, 65, 31, 43, 23, 69, 23, 71, 35, 39, 35
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OFFSET

1,5


COMMENTS



LINKS



FORMULA

a(n) = phi(n)  1 = A000010(n)  1.
a(n) = card({k k prime to n} setminus {k k divides n}).  Peter Luschny, Aug 05 2011
G.f.: x/(1  x) + Sum_{k >= 1} mu(k)*x^k/(1  x^k)^2.  Ilya Gutkovskiy, Mar 16 2017


EXAMPLE

a(9) = 5 because 2, 4, 5, 7, 8 are coprime to 9.
a(10) = 3 because 3, 7, 9 are coprime to 10.


MAPLE



MATHEMATICA



PROG



CROSSREFS



KEYWORD

nonn,easy


AUTHOR



EXTENSIONS



STATUS

approved



