Definition

1. A number sequence is an ordered list of numbers which follows a particular rule. 
2. Each number in the sequence is called a term. An example of a number sequence is shown below:
7, 9, 11, 13, 15, … 
First term = 7, second term = 9, third term = 11.
3. Most number sequences involve adding/subtracting or multiplying/dividing in the rule for finding one term from the one before it. Once we find the rule, we can use it to find the subsequent terms. 

Some special number sequences are shown below:

General Term in a Number Sequence

We can use the method of finding subsequent terms of a sequence to find the 50th or the 100th term, but it would be too tedious and time consuming. A faster method would thus be to find the general term, or the nth term first. 

The general term, or nth term of a sequence is an algebraic expression that allows us to find the value of any term in a sequence, e.g. the 100th term or the 299th term. 

If the common difference between terms in a number sequence is a constant, i.e. any term minus its immediate previous term gives the same constant, then we can use the following formula to find the nth term of a number sequence.