What is a quadratic sequence?

A quadratic sequence is where the second differences between each term are the same.

An example of a quadratic sequence is:

5, 9, 17, 29, 45.

The differences between each term are: 4, 8, 12, 16. The difference between these numbers is 3 and is the same each time. As the second difference is the same, this is a quadratic sequence.