Hecke's inverse cotangent numbers

Fuente: arXiv
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Autor principal: Girstmair, Kurt
Formato: Preprint
Publicado: 2025
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author Girstmair, Kurt
author_facet Girstmair, Kurt
contents In connection with Eisenstein series for the principal congruence subgroup $Γ(n)$, Hecke introduced certain numbers, of which he said that they are rational and cumbersome to calculate. We show, however, that these numbers are (essentially) generators of the $n$th cyclotomic field or its maximal real subfield. They arise from the well investigated {\em cotangent numbers} by matrix inversion, which is why we call them {\em inverse cotangent numbers}. We describe them as linear combinations of roots of unity with rational coefficients in a fairly closed form, provided that $n$ is square-free. We also exhibit a formula for these numbers in terms of generalized Bernoulli numbers and Gauss sums.
format Preprint
id arxiv_https___arxiv_org_abs_2503_01349
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Hecke's inverse cotangent numbers
Girstmair, Kurt
Number Theory
11R18
In connection with Eisenstein series for the principal congruence subgroup $Γ(n)$, Hecke introduced certain numbers, of which he said that they are rational and cumbersome to calculate. We show, however, that these numbers are (essentially) generators of the $n$th cyclotomic field or its maximal real subfield. They arise from the well investigated {\em cotangent numbers} by matrix inversion, which is why we call them {\em inverse cotangent numbers}. We describe them as linear combinations of roots of unity with rational coefficients in a fairly closed form, provided that $n$ is square-free. We also exhibit a formula for these numbers in terms of generalized Bernoulli numbers and Gauss sums.
title Hecke's inverse cotangent numbers
topic Number Theory
11R18
url https://arxiv.org/abs/2503.01349