## Key Equations

Formula for a factorial | [latex]\begin{align}0!&=1\\ 1!&=1\\ n!&=n\left(n - 1\right)\left(n - 2\right)\cdots \left(2\right)\left(1\right)\text{, for }n\ge 2\end{align}[/latex] |

## Key Concepts

- A sequence is a list of numbers, called terms, written in a specific order.
- Explicit formulas define each term of a sequence using the position of the term.
- An explicit formula for the [latex]n\text{th}[/latex] term of a sequence can be written by analyzing the pattern of several terms.
- Recursive formulas define each term of a sequence using previous terms.
- Recursive formulas must state the initial term, or terms, of a sequence.
- A set of terms can be written by using a recursive formula.
- A factorial is a mathematical operation that can be defined recursively.
- The factorial of [latex]n[/latex] is the product of all integers from 1 to [latex]n[/latex]

## Glossary

**explicit formula** a formula that defines each term of a sequence in terms of its position in the sequence

**finite sequence** a function whose domain consists of a finite subset of the positive integers [latex]\left\{1,2,\dots n\right\}[/latex] for some positive integer [latex]n[/latex]

**infinite sequence** a function whose domain is the set of positive integers

**n factorial** the product of all the positive integers from 1 to [latex]n[/latex]

**nth term of a sequence** a formula for the general term of a sequence

**recursive formula** a formula that defines each term of a sequence using previous term(s)

**sequence** a function whose domain is a subset of the positive integers

**term** a number in a sequence