This custom block tests if a number is a Fibonacci number. Generating Fibonacci numbers in the project is slow because it tests every number. This method allows you to generate Fibonacci numbers starting from any number. If you want a fast Fibonacci number generator that allows you to start from any number, you can use this method to generate the first two numbers and add them together, etc.
I was inspired to make this by a question on Quora and because I was bored. Basically, a number is a Fibonacci number if (5n^2+4) or (5n^2-4) is a perfect square. To check if the result is a perfect square, I get the square root of the result % 1. If result of that is 0, then it is a perfect square!