Subgroups of finite index in a free product with amalgamated subgroup

Stothers, W. W.

doi:10.1090/S0025-5718-1981-0606522-9

Subgroups of finite index in a free product with amalgamated subgroup
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Math. Comp. 36 (1981), 653-662 Request permission

Abstract:

Let G be a free product of finitely many finite groups with amalgamated subgroup. Using coset diagrams, a recurrence relation is obtained for the number of subgroups, and of free subgroups, of each finite index in G. In the latter case, an asymptotic formula is derived. When the amalgamated subgroup is central, the relation takes a simpler form.

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