CAOP

\[ \begin{align} L_n^{(a)}(x;q) &= \frac{(q^{a+1};q)_n}{(q;q)_n} \sum_{k=0}^\infty \frac{(q^{-n};q)_k}{(q^{a+1};q)_k (q;q)_k} q^{k \choose 2} \left(q^{n+a+1}x\right)^k\\ &= \frac{(q^{a+1};q)_n}{(q;q)_n} {}_{1}\phi_{1}\!\left(\left. {q^{-n} \atop q^{a+1}} \; \right| q ; -q^{n+a+1}x \right) \end{align} \]