I came across the following line and was wondering what it meant exactly and how you go about showing it. Let d be a fundamental discriminant. Let P(d) = the divisors of d except for the largest.
The cardinality of P(d) is at most the 2-adic valuation of the h (the class number).
I only have a vague notation of what is meant by the 2-adic valuation, so any clarification on that as well as how to prove the statement would be helpful. Thank you.