The summation notation, also known as sigma notation, allows long sums to be written in a compact way. It is denoted using the Greek letter sigma along with several other pieces of information about the summation.
The variable is called the summation index and only takes integer values. To write this sum explicitly, the variable appearing after sigma must be substituted with the integers from the initial value through the last value. Notice some aspects of summation notation:
The summation notation is not only useful for working with sums involving a large number of terms, but it can also be used to represent an infinite sum.