On Dirichlet eigenvalues of regular polygons

We prove that the first Dirichlet eigenvalue of a regular $N$-gon of area $π$ has an asymptotic expansion of the form $λ_1(1+\sum_{n\ge3}C_n(λ_1)N^{-n})$ as $N\to\infty$, where $λ_1$ is the first Dirichlet eigenvalue of the unit disk and $C_n$ are polynomials whose coefficients belong to the space of multiple zeta values of weight $n$. We also explicitly compute these polynomials for all $n\le14$.