\[R_{-a}\left(b_{1},\dots,b_{n};0,z_{2},\dots,z_{n}\right)=\frac{\mathrm{B}\left%
(a,a^{\prime}-b_{1}\right)}{\mathrm{B}\left(a,a^{\prime}\right)}R_{-a}\left(b_%
{2},\dots,b_{n};z_{2},\dots,z_{n}\right),\]