Pi notation

Pi notation is a method used to represent the product of terms. It is similar to Sigma notation but uses a capital letter Pi.

Definition

For any integers $m$ and $n$ such that $m \leq n$ and any function $a(x)$ defined on the integers, we write $\sum_{k=m}^n a(k)$ for the product $a(m)\cdot a(m+1)\cdot a(m+2)\cdot a(m+3)\cdots a(n-1)\cdot a(n)$.