Summation Notation is a mathematical notation for finding the sum of the terms of any sequence. The mathematical symbol for summation is the Greek letter sigma, . In the previous book we used the following example to denote the sum of the first five terms of a sequence: . The notation that describes the summation of the first term through the fifth term of a sequence is . Therefore, .

The notation for the sum of n terms is . In summation notation, the letter n is called the index of summation . The value below the sigma represents the initial term. The value above the sigma represents the final term. a_{n} represents the explicit formula for the sequence.