A329272 Number of octic primitive Dirichlet characters modulo n.

1, 0, 1, 1, 3, 0, 1, 2, 0, 0, 1, 1, 3, 0, 3, 4, 7, 0, 1, 3, 1, 0, 1, 2, 0, 0, 0, 1, 3, 0, 1, 8, 1, 0, 3, 0, 3, 0, 3, 6, 7, 0, 1, 1, 0, 0, 1, 4, 0, 0, 7, 3, 3, 0, 3, 2, 1, 0, 1, 3, 3, 0, 0, 0, 9, 0, 1, 7, 1, 0, 1, 0, 7, 0, 0, 1, 1, 0, 1, 12, 0, 0, 1, 1, 21, 0, 3, 2, 7, 0, 3

Offset: 1

Author

Jianing Song, Nov 10 2019

Keywords

• nonn
• mult

Comments

a(n) is the number of primitive Dirichlet characters modulo n such that all entries are 0 or a eighth-power root of unity (+-1, +-i, +-sqrt(2)/2 +- sqrt(2)/2*i, i = sqrt(-1)).

Mobius transform of A247257.

Examples

			Let w = exp(2*Pi*i/8) = sqrt(2)/2 + i*sqrt(2)/2. For n = 17, the 7 octic primitive Dirichlet characters modulo n are:
  Chi_1 = [0, 1, -i, w, -1, -w, -w^3, w^3, i, i, w^3, -w^3, -w, -1, w, -i, 1];
  Chi_2 = [0, 1, -1, i, 1, i, -i, -i, -1, -1, -i, -i, i, 1, i, -1, 1];
  Chi_3 = [0, 1, i, w^3, -1, -w^3, -w, w, -i, -i, w, -w, -w^3, -1, w^3, i, 1];
  Chi_4 = [0, 1, 1, -1, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, -1, 1, 1];
  Chi_5 = [0, 1, -i, -w, -1, w, w^3, -w^3, i, i, -w^3, w^3, w, -1, -w, -i, 1];
  Chi_6 = [0, 1, -1, -i, 1, -i, i, i, -1, -1, i, i, -i, 1, -i, -1, 1];
  Chi_7 = [0, 1, i, -w^3, -1, w^3, w, -w, -i, -i, -w, w, w^3, -1, -w^3, i, 1],
so a(17) = 7.
		

Links

• Jianing Song, Table of n, a(n) for n = 1..65539

Crossrefs

Number of k-th power primitive Dirichlet characters modulo n: A114643 (k=2), A160498 (k=3), A160499 (k=4), A307380 (k=5), A307381 (k=6), A307382 (k=7), this sequence (k=8).

Cf. A247257 (number of solutions to x^8 == 1 (mod n)).

Programs

Mathematica

f[2, e_] := If[2 <= e <= 5, 2^(e-2), 0]; f[p_, e_] := If[e == 1, GCD[p-1, 8] - 1, 0];  a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 16 2020 *)

PARI

a(n)={
    my(r=1, f=factor(n));
    for(j=1, #f[, 1], my(p=f[j, 1], e=f[j, 2]);
        if(p==2, if(e>=2&&e<=5, r*=2^(e-2), r=0; return(r)));
        if(p>2, if(e==1, r*=gcd(p-1,8)-1, r=0; return(r)));
    );
    return(r);
}

Formula

Multiplicative with a(2^e) = 2^(e-2) for 2 <= e <= 5, a(2^e) = 0 for e = 1 or e >= 6; a(p^e) = gcd(p-1, 8)-1 if p > 2 and e = 1, a(p^e) = 0 if p > 2 and e >= 2.