The document discusses Fibonacci numbers, which are an integer sequence where each number is the sum of the two preceding ones, starting from 0 and 1. It describes how the sequence is named after Leonardo of Pisa, also known as Fibonacci. It also discusses how the golden ratio of approximately 0.618 is related to Fibonacci numbers. The document then explores different algorithms to calculate Fibonacci numbers and their time complexities, such as a naive recursive method, bottom-up dynamic programming, and using a formula involving the golden ratio. It notes some potential issues like bounds checking for integer overflow.