Weighted Hardy Inequality in $l_2$

Abstract

We study the behaviour of the smallest possible constant $d_n$ in weighted Hardy inequality $$ \sum_{k=1}^{n}\Big(\frac{1}{k}\sum_{j=1}^{k}a_j\Big)^2 k^ε\le d(n,ε)\,\sum_{k=1}^{n}{a_k^2}\,k^ε$$ The exact rate of convergence of $d_n$ is established and the ``almost extremal'' sequence is found.