The best constant in a Hilbert-type inequality

Abstract

We establish that \[\sum_{m=1}^\infty \sum_{n=1}^\infty a_m \overline{a_n} \frac{mn}{(\max(m,n))^3} \leq \frac{4}{3}\sum_{m=1}^\infty |a_m|^2\] holds for every square-summable sequence of complex numbers $a=(a_1,a_2,\dots )$ and that the constant $4/3$ cannot be replaced by any smaller number. Our proof is rooted in a seminal 1911 paper concerning bilinear forms due to Schur, and we include for expositional reasons an elaboration on his approach.

References in corpus (2)

• Sharp norm estimates for composition operators and Hilbert-type inequalities
• The spectrum of some Hardy kernel matrices