Working with the various special functions of mathematical physics and applied mathematics we often encounter inverse relations of the type $F_n(x)=sumlimits_{k=0}^{n}A^n_kG_k(x)$ and $ G_n(x)=sumlimits_{k=0}^{n}B_k^nF_k(x)$, where 0, 1, 2,$cdots$. Here $F_n(x)$, $G_n(x)$ denote special polynomial functions, and $A_k^n$, $B_k^n$ denote coefficients found by use of the orthogonal properties of $F_n(x)$ and $G_n(x)$, or by skillful series manipulations. Typically $G_n(x)=x^n$ and $F_n(x)=P_n(x)$, the n-th Legendre polynomial. We give a collection of inverse series pairs of the type $f(n)=sumlimits_{k=0}^{n}A_k^ng(k)$ if and only if $g(n)=sumlimits_{k=0}^{n}B_k^nf(k)$, each pair being based on some reasonably well-known special function. We also state and prove an interesting generalization of a theorem of Rainville in this form.