##  [Class Number](/class-number) 

  ##  [Class Number](https://puremath.quantumdictionary.io/class-number-0) 

  

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- Mathematics & Logic -

**Pure Mathematics Dictionary**

 







 

 

 

 



 

 

 

 

Definition

The cardinality of the ideal class group of a number field or Dedekind domain; it counts distinct equivalence classes of nonzero fractional ideals under principal ideal equivalence and thus quantifies the failure of every ideal to be principal.