MathItems

The quantity $\binom{n}{k}$ is called a binomial-coefficient.

For real $r$ we have

$$\binom{r}{k} = \prod_{j=1}^k \frac{r + 1 - j}{j}$$

for integer $k \geq 0$ and

$$\binom{r}{k} = 0$$

for integer $k < 0$.