Abstract
We consider a cuspidal class number, which is the order of a subgroup of the full cuspidal divisor class group of X 1(Np n) with \({p\nmid N}\) and n ≥ 1. By studying the second generalized Bernoulli numbers, we obtain results similar to ones (Ferrero and Washington in Ann Math (2) 109(2):377–395, 1979; Washington in Invent Math 49:87–97, 1978) about the relative class numbers of cyclotomic \({\mathbb{Z}_p}\)-extension of an abelian number field.
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Sun, HS. Cuspidal class number of the tower of modular curves X 1(Np n). Math. Ann. 348, 909–927 (2010). https://doi.org/10.1007/s00208-010-0505-7
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DOI: https://doi.org/10.1007/s00208-010-0505-7