Given a Number N check if it part of Fibonacci Series or Not?

#1

I am unable to frame a flowchart for this question
When searched on the net it is showing that if N satisfies this formula(5nn-4)[where nis the square root of N] then it is a part of Fibonacci series but I couldn’t get it through.

#2

@shivamkejriwal,
Its maths, you can see this_wiki 's identification section for a formal proof.

#3

Thanks Abhijit for the guidance.