A bseries/b means adding up numbers within a sequence.

Sigma notation is shorthand for summing up a series.

For example:

(\displaystyle\sum_^n 1 = \overbrace{1+1+...+1+1}^{\text{n times}} = n)

(\displaystyle\sum_^n r = \dfrac{n(n+1)}{2})

(\displaystyle\sum_^5 r^2 = 1^2 + 2^2 + 3^2 + 4^2 + 5^2 = 55 )

[b]uGeneral result[/u]/b

(\displaystyle\sum_^n f(x) = f(1) + f(2) + ... + f(n-1) + f(n) )

(\displaystyle\sum_^n f(x) = f(1) + f(2) + ... + f(n-1) + f(n) )