Normal zeta function of a group: Difference between revisions
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<math>\zeta_G(s) = \sum_{n=1}^{\infty} a_n(G)n^{-s}</math> | <math>\zeta_G(s) = \sum_{n=1}^{\infty} a_n(G)n^{-s}</math> | ||
where <math>a_n(G)</math> denotes the number of normal | where <math>a_n(G)</math> denotes the number of [[normal subgroup]]s of <math>G</math> of [[index of a subgroup|index]] <math>n</math>. Equivalently, it is: | ||
<math>\sum_{H \underline{\triangleleft}_f G} [G:H]^{-s}</math> | <math>\sum_{H \underline{\triangleleft}_f G} [G:H]^{-s}</math> | ||
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* [[Zeta function of a group]] | * [[Zeta function of a group]] | ||
==References== | |||
===Journal references=== | |||
* {{paperlink|GrunewaldSegalSmith}} | |||
Latest revision as of 23:14, 16 August 2013
Definition
Let be a group. The normal zeta function of is defined as:
where denotes the number of normal subgroups of of index . Equivalently, it is:
summing up over all normal subgroups of finite index in .
The coefficients are all finite when the group is finitely generated. This follows from finitely generated implies finitely many homomorphisms to any finite group (see also group with finitely many homomorphisms to any finite group).
Related notions
References
Journal references
- Subgroups of finite index in nilpotent groups by F. J. Grunewald, D. Segal and G. C. Smith, Inventiones mathematicae, Volume 93,Number 1, Page 185 - 223(Year 1988): Gated copy (PDF)More info