What is the Fibonacci sequence?

In a nutshell

Fibonacci sequence is the series of numbers that start with 0 and 1 and take the following pattern:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

After the first two numbers (0 and 1), you find the next number by adding the preceding two numbers.

Implementation in code

See this post.