Hello Friends, today I want to give you a basic information that is very useful in letting know whether the number is a fibonacci number just by simple formula.

Here it goes,

Let us suppose we have to check whether the number

Here it goes,

Let us suppose we have to check whether the number

**n**is a fibonacci number or not, then the condition**5n^2 + 4 or 5n^2 - 4**should be a perfect square.// A utility function that returns true if x is perfect square bool isPerfectSquare(int x) { int s = sqrt(x); return (s*s == x); } // Returns true if n is a Fibinacci Number, else false bool isFibonacci(int n) { // n is Fibinacci if one of 5*n*n + 4 or 5*n*n - 4 or both // is a perferct square return isPerfectSquare(5*n*n + 4) || isPerfectSquare(5*n*n - 4); } int main() { for (int i = 1; i <= 10; i++) isFibonacci(i)? cout << i << " is a Fibonacci Number \n": cout << i << " is a not Fibonacci Number \n" ; return 0; }

Now once you pass the number to the function it will tell you whether or not the number is a part of fibonacci series or not.

Thanks

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