On the approximation of the zeta function by Dirichlet polynomials
Juan Arias de Reyna
Abstract
We prove that for $s=σ+it$ with $σ\ge0$ and $0<t\le x$, we have \[ζ(s)=\sum_{n\le x}n^{-s}+\frac{x^{1-s}}{(s-1)}+Θ\frac{29}{14} x^{-σ},\qquad \frac{29}{14}=2.07142\dots\] where $Θ$ is a complex number with $|Θ|\le1$. This improves Theorem 4.11 of Titchmarsh.
