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## program solution

// C++ program to check if x is a perfect square

#include <iostream>
#include <math.h>
using namespace std;

// 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);

// A utility function to test above functions
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;

## Output

1 is a Fibonacci Number

2 is a Fibonacci Number

3 is a Fibonacci Number

4 is a not Fibonacci Number

5 is a Fibonacci Number

6 is a not Fibonacci Number

7 is a not Fibonacci Number

8 is a Fibonacci Number

9 is a not Fibonacci Number

10 is a not Fibonacci Number

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