A series is the indicated sum of the terms of a sequence The symbol which is the Greek letter sigma is used to indicate a sum The number of minutes that Ken walked on the nth day is a 20 n 1 5 We can write the sum of the number of minutes that Ken walked in sigma notation 14 14 a 20 n 1 5 n 1 n 1 The n 1 below is the value of n for the first term of the series and the number above is the value of n for the last term of the series The symbol 14 a can be read as the sum of a for all integral values of n from 1 to 14 n 1