For non‑negative integers \( n \) and \( k \) with \( 0 \le k \le n \):
where \( m! = m \times (m-1) \times \cdots \times 2 \times 1 \) and \( 0! = 1 \).
Symmetry: \( \binom{n}{k} = \binom{n}{n-k} \).
Edge cases: \( \binom{n}{0} = \binom{n}{n} = 1 \).
\( \displaystyle \binom{n}{k} = \frac{n!}{k!\,(n-k)!} \) → substitute n,k → evaluate