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 3^{1} + 3^{2} + 3^{3} + 3^{4} + 3^{5} 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.