CAOP

\[ \begin{align} K_n(q^{-x};p,N;q) &= \sum_{k=0}^\infty \frac{(q^{-n};q)_k (q^{-x};q)_k (-pq^n;q)_k}{(q^{-N};q)_k (q;q)_k} q^k\\ &= {}_{3}\phi_{2}\!\left(\left. {q^{-n}, q^{-x}, -pq^n \atop q^{-N}, 0} \; \right| q ; q \right) \end{align} \]