A114811 - OEIS

A114811

Number of real, weakly primitive Dirichlet characters modulo n.

1, 1, 2, 1, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 4, 0, 2, 0, 2, 2, 4, 2, 2, 4, 0, 2, 0, 2, 2, 4, 2, 0, 4, 2, 4, 0, 2, 2, 4, 4, 2, 4, 2, 2, 0, 2, 2, 0, 0, 0, 4, 2, 2, 0, 4, 4, 4, 2, 2, 4, 2, 2, 0, 0, 4, 4, 2, 2, 4, 4, 2, 0, 2, 2, 0, 2, 4, 4, 2, 0, 0, 2, 2, 4, 4, 2, 4, 4, 2, 0, 4, 2, 4, 2, 4, 0, 2, 0, 0, 0, 2, 4, 2, 4, 8

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OFFSET

1,3

COMMENTS

Any primitive Dirichlet character is weakly primitive (not conversely). Jager uses the phrase "proper character", but this conflicts with other authors (e.g., W. Ellison and F. Ellison, Prime Numbers, Wiley, 1985, p. 224) who use the word "proper" to mean the same as "primitive".

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

H. Jager, On the number of Dirichlet characters with modulus not exceeding x, Nederl. Akad. Wetensch. Proc. Ser. A 76 = Indag. Math. 35 (1973) 452-455.

FORMULA

a(n) = sum A114643(n/d), where the sum is over all divisors 1<=d<=n of A055231(n).

This sequence is multiplicative with a(2)=1, a(4)=1, a(8)=2, a(2^r)=0 for r>2, a(p)=2 for prime p>2 and a(p^r)=0 for r>1. - Steven Finch, Mar 08 2006

EXAMPLE

The function chi defined on the integers by chi(1)=1, chi(5)=-1 and chi(2)=chi(3)=chi(4)=chi(6)=0 [and extended periodically] is a weakly primitive character mod 6, but not mod 12 or mod 18. In this sense, we eliminate the "overcounting" of real Dirichlet characters in A060594.

MATHEMATICA

rad[n_] := Times @@ First /@ FactorInteger[n]; A055231[n_] := Denominator[ n/rad[n]^2 ]; A114643[n_] := Sum[ MoebiusMu[n/d] * Sum[ If[ Mod[i^2 - 1, d] == 0, 1, 0], {i, 2, d}], {d, Divisors[n] } ]; A114643[1] = 1; a[n_] := Sum[ A114643[n/d], {d, Divisors[ A055231[n] ] } ]; Table[a[n], {n, 1, 105}] (* Jean-François Alcover, Jun 20 2013 *)

f[p_, e_] := 0; f[p_, 1] = 2; f[2, e_] := 0; f[2, 1] = f[2, 2] = 1; f[2, 3] = 2; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Jan 11 2023 *)

PROG

(PARI)

A055231(n) = {my(f=factor(n)); for (k=1, #f~, if (f[k, 2] > 1, f[k, 2] = 0); ); factorback(f); } \\ From A055231

A114643(n) = sum(d=1, n, if(n%d==0, moebius(n/d)*sum(i=1, d, if((i^2-1)%d, 0, 1)), 0)); \\ From A114643

A114811(n) = sumdiv(A055231(n), d, A114643(n/d)); \\ Antti Karttunen, Sep 27 2018

(PARI)

A114811(n) = { my(f=factor(n)); for(i=1, #f~, if(2==f[i, 1], if(f[i, 2]<3, f[i, 2]=0, if(3==f[i, 2], f[i, 2]=1, f[i, 1]=0)), if(f[i, 2]>1, f[i, 1]=0, f[i, 1]=2))); factorback(f); }; \\ Antti Karttunen, Sep 27 2018, after Steven Finch's multiplicative formula.

CROSSREFS

Cf. A055231, A060594, A114643.

Sequence in context: A318450 A120256 A300647 * A275675 A219025 A270746

Adjacent sequences: A114808 A114809 A114810 * A114812 A114813 A114814

KEYWORD

nonn,mult

AUTHOR

Steven Finch, Feb 19 2006

STATUS

approved