what greek letter is used to denote a series?

It might be omega symbolized by Ù or ù but I would wait for another answer.

Sorry the symbols didn't come out. If you look on wikipedia and search "omega" you'll find the symbols I'm talking about.

The Greek letter sigma (Σ) is commonly used to represent a series in mathematics. The symbol is used to denote the sum of a sequence of numbers. For example, if you have a series of numbers a₁, a₂, a₃, ..., aₙ, then the sum of these numbers can be represented as Σaᵢ, where i ranges from 1 to n.

If you want to type the Greek letter sigma (Σ) on a computer, you have a few options:

1. Keyboard Shortcut: On Windows, you can press and hold the ALT key, then type 229 on the numeric keypad (Σ). On Mac, you can press and hold the Option key, then press the letter S (Σ).

2. Character Map: On Windows, you can use the "Character Map" application to find and copy the Greek letter sigma (Σ) to your clipboard. On Mac, you can use the "Character Viewer" or "Emoji & Symbols" tool to find and insert the sigma symbol (Σ).

3. LaTeX or MathML: If you are working with mathematical notation in a document or on a website, you can use LaTeX or MathML to represent the Greek letter sigma (Σ). For example, in LaTeX, you can use the command \sum or \Sigma to display the sigma symbol (Σ).