The **narrow class number** of an algebraic number field is the order of its narrow class group.
Since the ordinary ideal class group is a quotient of the narrow class group, the narrow class number is a multiple of the class number. Moreover, the ratio is a power of $2$. The two class numbers are the same in many cases, for example when the number field is totally complex.

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- Last edited by David Roberts on 2019-04-30 17:02:37

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- 2019-04-30 17:02:37 by David Roberts (Reviewed)
- 2018-07-08 00:26:59 by Alina Bucur (Reviewed)

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