The expansion of a finite number of terms of the Gauss hypergeometric function of unit argument and the Landau constants

We obtain convergent inverse factorial expansions for the sum $S_n(a,b;c)$ of the first $n$ terms of the Gauss hypergeometric function of unit argument valid for $n\ge 1$. The form of these expansions depends on the location of the parametric excess $s:=c-a-b$ in the complex $s$-plane. The leading behaviour as $n\to \mathrm{\infty }$ agrees with previous results in the literature. The case $a=b=1\mathrm{/}2$, $c=1$ corresponds to the Landau contants.