Test if a number is fibonacci

Question

I know how to make the list of the Fibonacci numbers, but i don\'t know how can i test if a given number belongs to the fibonacci list - one way that comes in mind is genera

Answer 1

A positive integer ω is a Fibonacci number if and only if either 5ω² + 4 or 5ω² - 4 is a perfect square.

See The Fabulous Fibonacci Numbers for more.