SECTION 5

A sequence is a list of numbers which are related to each other. Each item of the sequence is called a term.
Invariably, this being Mathematics, there is a formula which generates each term of the sequence.

Notation
We use the notation Un to denote the nth term of a sequence. The subscript of the letter U tells you which term you are finding.
Thus U1 is the first term, U2 is the second term, U3 is the third and so on.
Just as the term before U8 is U7 , and the term after U8 is U9,
so the term before Un is Un–1 and the term after Un is Un+1.