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 A109606 Number of numbers k with 1 < k < n which are relatively prime to n. 5
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Number of nonprincipal Dirichlet characters mod n. - Charles R Greathouse IV, Jul 25 2013 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 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 A109606 := n -> numtheory[phi](n) - 1: # Peter Luschny, Aug 05 2011 MATHEMATICA EulerPhi[Range[80]] - 1 (* Alonso del Arte, Sep 16 2017 *) PROG (PARI) a(n)=eulerphi(n)-1 \\ Charles R Greathouse IV, Jul 25 2013 (MAGMA) [EulerPhi(n)-1: n in [1..80]]; // Vincenzo Librandi, Sep 16 2017 CROSSREFS Cf. A000010. Sequence in context: A071168 A091926 A325685 * A318727 A307806 A127418 Adjacent sequences:  A109603 A109604 A109605 * A109607 A109608 A109609 KEYWORD nonn,easy AUTHOR Andrew Weimholt, Jul 31 2005 EXTENSIONS Definition modified by Reinhard Zumkeller, Mar 03 2009 Offset set to 1, in accordance to A000010, by Peter Luschny, Aug 05 2011 STATUS approved

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Last modified March 28 11:49 EDT 2020. Contains 333083 sequences. (Running on oeis4.)