#### notes

Let `a_1, a_2, a_3,…,a_n`, be a given sequence. Then, the expression

`a_1 + a_2 + a_3 +,…+ a_n + ...`

is called the series associated with the given sequence.

Series are often represented in compact form, called sigma notation, using the Greek letter ∑(sigma) as means of indicating the summation involved.

Thus the series `a_1 + a_2 + a_3 +...+a_n` is abbreviated as `sum _(k=1)^n a_k.`