In Year 9 Mathematics, we learn about sequences. A sequence is just a list of numbers that follow a certain rule. Each number in this list is called a term.

Notation:

• We usually write the first term as $a_1$, the second term as $a_2$, and keep going.
• For example, if we have the sequence $2, 4, 6, 8...$, we can show this with the formula $a_n = 2n$. Here, $n$ tells us which term it is.

Example:

• Take the sequence of odd numbers: $1, 3, 5, 7...$. We can describe it with the formula $a_n = 2n - 1$.

Remember, sequences can have a set number of terms (finite) or go on forever (infinite). They are a fun way for us to see patterns in numbers!