Sigma notation uses the Greek letter capital sigma, ∑ to show that the members of a sequence must be added.
Think of ∑ as meaning "the sum of".
e.g. 
means add together the four terms made by putting n = 1, n = 2, n = 3 and n = 4 into the expression 2n + 3
 |
= (2 x 1 + 3) + (2 x 2 + 3) + (2 x 3 + 3) + (2 x 4 + 3) |
| = 5 + 7 + 9 + 11 | |
| = 32 |
A mathematical series is obtained by adding the terms of a sequence of numbers together.
The next two topics cover arithmetic series and geometric series.
A given series can be written in sigma notation.
The series 31 + 32 + 33 + 34 + 35 could be written as 
Sometimes if the variable is obvious, as above, where it is n, then the n may not be displayed above and below the sigma symbol.
