A319660 - OEIS

A319660

2-rank of the class group of imaginary quadratic field with discriminant -k, k = A039957(n).

0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 2, 0, 1, 0, 1, 1, 0, 0, 2, 1, 0, 1, 0, 2, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 2, 1, 1, 1, 1, 0

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,41

COMMENTS

The p-rank of a finite abelian group G is equal to log_p(#{x belongs to G : x^p = 1}) where p is a prime number. In this case, G is the class group of Q(sqrt(-k)), and #{x belongs to G : x^p = 1} is the number of genera of Q(sqrt(-k)) (cf. A003641).

LINKS

Table of n, a(n) for n=1..87.

Rick L. Shepherd, Binary quadratic forms and genus theory, Master of Arts Thesis, University of North Carolina at Greensboro, 2013.

FORMULA

a(n) = log_2(A003641(n)) = omega(A039957(n)) - 1, where omega(k) is the number of distinct prime divisors of k.

PROG

(PARI) for(n=1, 1000, if(n%4==3 && issquarefree(n), print1(omega(n) - 1, ", ")))

CROSSREFS

Cf. A003641, A039957, A319659, A319661.

Sequence in context: A226206 A350682 A375150 * A285726 A285005 A263074

Adjacent sequences: A319657 A319658 A319659 * A319661 A319662 A319663

KEYWORD

nonn

AUTHOR

Jianing Song, Sep 25 2018

STATUS

approved