A307381 Number of sextic primitive Dirichlet characters modulo n.

1, 0, 1, 1, 1, 0, 5, 2, 4, 0, 1, 1, 5, 0, 1, 0, 1, 0, 5, 1, 5, 0, 1, 2, 0, 0, 0, 5, 1, 0, 5, 0, 1, 0, 5, 4, 5, 0, 5, 2, 1, 0, 5, 1, 4, 0, 1, 0, 0, 0, 1, 5, 1, 0, 1, 10, 5, 0, 1, 1, 5, 0, 20, 0, 5, 0, 5, 1, 1, 0, 1, 8, 5, 0, 0, 5, 5, 0, 5, 0, 0, 0, 1, 5, 1, 0, 1

Offset

1,7

Comments

a(n) is the number of primitive Dirichlet characters modulo n such that all entries are 0 or a six-power root of unity (1, (1 + sqrt(3)*i)/2, (-1 + sqrt(3)*i)/2), -1, (-1 - sqrt(3)*i)/2, (1 - sqrt(3)*i)/2)).

Mobius transform of A319100.

Links

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

Formula

Multiplicative with a(4) = 1, a(8) = 2, a(2^e) = 0 for e = 1 or e >= 4; a(3) = 1, a(9) = 4, a(3^e) = 0 for e >= 3; a(p) = 5 if p == 1 (mod 6) and 1 if p == 5 (mod 6), a(p^e) = 0 if p > 3 and e >= 2.

Example

Let w = exp(2*Pi/6) = (1 + sqrt(3)*i)/2. For n = 19, the 5 sextic primitive Dirichlet characters modulo n are:
  Chi_1 = [0, 1, w, w, w - 1, -w, w - 1, 1, -1, w - 1, -w + 1, 1, -1, -w + 1, w, -w + 1, -w, -w, -1];
  Chi_2 = [0, 1, w - 1, w - 1, -w, w - 1, -w, 1, 1, -w, -w, 1, 1, -w, w - 1, -w, w - 1, w - 1, 1];
  Chi_3 = [0, 1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1];
  Chi_4 = [0, 1, -w, -w, w - 1, -w, w - 1, 1, 1, w - 1, w - 1, 1, 1, w - 1, -w, w - 1, -w, -w, 1];
  Chi_5 = [0, 1, -w + 1, -w + 1, -w, w - 1, -w, 1, -1, -w, w, 1, -1, w, -w + 1, w, w - 1, w - 1, -1],
so a(19) = 5.

Mathematica

f[2, e_] := Which[e == 1, 0, e == 2, 1, e == 3, 2, e >= 4, 0]; f[3, e_] := Which[e == 1, 1, e == 2, 4, e >= 3, 0]; f[p_, 1] := If[Mod[p, 6] == 1, 5, 1]; f[p_, e_] := 0; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 16 2020 *)

Prog

(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==3, r*=2, if(e!=2, r=0; return(r))));
        if(p==3, if(e==2, r*=4, if(e!=1, r=0; return(r))));
        if(p>3, if(p%6==1&&e==1, r*=5, if(e!=1, r=0; return(r))));
    );
    return(r);
} \\ Jianing Song, Nov 10 2019

Crossrefs

Number of k-th power primitive Dirichlet characters modulo n: A114643 (k=2), A160498 (k=3), A160499 (k=4), A307380 (k=5), this sequence (k=6), A307382 (k=7), A329272 (k=8).

Cf. A319100 (number of solutions to x^6 == 1 (mod n)).

Sequence in context: A350518 A214662 A277581 * A256167 A207528 A019901

Adjacent sequences: A307378 A307379 A307380 * A307382 A307383 A307384

Keyword

nonn,mult

Author

Jianing Song, Apr 06 2019

Status

approved