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 A111725 Number of residues modulo n of the maximum order. 10
 1, 1, 1, 1, 2, 1, 2, 3, 2, 2, 4, 3, 4, 2, 4, 4, 8, 2, 6, 4, 6, 4, 10, 7, 8, 4, 6, 6, 12, 4, 8, 8, 12, 8, 8, 6, 12, 6, 8, 8, 16, 6, 12, 12, 8, 10, 22, 8, 12, 8, 16, 8, 24, 6, 16, 14, 18, 12, 28, 8, 16, 8, 24, 16, 24, 12, 20, 16, 30, 8, 24, 14, 24, 12, 16, 18, 24, 8, 24, 24, 18, 16, 40, 14, 32, 12 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS The maximum order modulo n is given by A002322(n). a(n) is the number of primitive lambda-roots of n. - Michel Marcus, Mar 17 2016 A primitive lambda-root is an element of maximal order modulo n. - Joerg Arndt, Mar 19 2016 a(n) is odd if and only if n is a factor of 24, i.e., n is in A018253. - Jianing Song, Apr 27 2019 LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 P. J. Cameron and D. A. Preece, Notes on primitive lambda-roots, 2009. P. J. Cameron and D. A. Preece, Primitive lambda-roots, 2014. R. D. Carmichael, Note on a new number theory function, Bull. Amer. Math. Soc. 16 (1909-10), 232-238. S. R. Finch, Idempotents and Nilpotents Modulo n, arXiv:math/0605019 [math.NT], 2006-2017. S. Li, On the number of elements with maximal order in the multiplicative group modulo n, Act. Arithm. 86 (2) (1998) 113, Theorem 2.1 FORMULA For prime n, a(n) = phi(phi(n)) = A010554(n) = phi(n-1). - Nick Hobson (nickh(AT)qbyte.org), Jan 09 2007 Decompose (Z/nZ)* as a product of cyclic groups C_{k_1} x C_{k_2} x ... x C_{k_m}, where k_i divides k_j for i < j, then a(n) = Sum_{d divides psi(n)} (mu(psi(n)/d)*Product{i=1..m} gcd(d, k_i)). This is an immediate corollary from the fact that the number of elements in (Z/nZ)* such that x^d == 1 (mod n) is Product{i=1..m} gcd(d, k_i). Here (Z/nZ)* is the multiplicative group of integers modulo n, psi(n) = A002322(n) and mu(n) = A008683(n). - Jianing Song, Apr 27 2019 MAPLE LiDelta := proc(q, n)     local a, p, e, lam, v ;     a := 0 ;     lam := numtheory[lambda](n) ;     for p in numtheory[factorset](n) do         e := padic[ordp](n, p) ;         if p =2 and e= 3 and q =2 and padic[ordp](lam, q) = 1 then             return A083399(n) ;         elif isprime(q) then             v := padic[ordp](lam, q) ;             if modp( numtheory[lambda](p^e), q^v) = 0 then                 a := a+1 ;             end if;         end if:     end do:     a ; end proc: A111725 := proc(n)     local a, q ;     a := 1;     for q in numtheory[factorset](numtheory[lambda](n)) do         a := a*(1-1/q^LiDelta(q, n)) ;     end do:     a*numtheory[phi](n) ; end proc: seq(A111725(n), n=1..30) ; # R. J. Mathar, Sep 29 2017 MATHEMATICA f[list_]:=Count[list, Max[list]]; Map[f, Table[Table[MultiplicativeOrder[k, n], {k, Select[Range[n], GCD[#, n]==1&]}], {n, 1, 100}]]  (* Geoffrey Critzer, Jan 26 2013 *) PROG (PARI) { a(n) = my(r, c, r1); r=1; c=0; for(k=0, n-1, if(gcd(k, n)!=1, next); r1=znorder(Mod(k, n)); if(r1==r, c++); if(r1>r, r=r1; c=1) ); c; } CROSSREFS Cf. A002322, A008330, A300064, A300065, A300079, A300080. Sequence in context: A117910 A275435 A029267 * A302257 A324748 A320387 Adjacent sequences:  A111722 A111723 A111724 * A111726 A111727 A111728 KEYWORD nonn AUTHOR Max Alekseyev, Nov 18 2005 STATUS approved

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Last modified June 23 07:38 EDT 2021. Contains 345395 sequences. (Running on oeis4.)