Q-Binomial coefficient
From specialfunctionswiki
The $q$-Binomial coefficient ${n \brack k}_q$ is $${n \brack k}_q = \dfrac{(q;q)_n}{(q;q)_k(q;q)_{n-k}},$$ where $(q;q)_{\xi}$ denotes the q-Pochhammer symbol.
Properties
q-Pochhammer as sum of q-binomial coefficients
