Given a number \’n\’, how to check if n is a Fibonacci number. First few Fibonacci numbers are 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 141, ..

Examples :

Input : 8 Output : Yes Input : 34 Output : Yes Input : 41 Output : No

Following is an interesting property about Fibonacci numbers that can also be used to check if a given number is Fibonacci or not.*A number is Fibonacci if and only if one or both of (5*n ^{2} + 4) or (5*n^{2} – 4) is a perfect square* (Source: Wiki).

`# python program to check if x is a perfect square` `import` `math` ` ` `# A utility function that returns true if x is perfect square` `def` `isPerfectSquare(x):` ` ` `s ` `=` `int` `(math.sqrt(x))` ` ` `return` `s` `*` `s ` `=` `=` `x` ` ` `# Returns true if n is a Fibinacci Number, else false` `def` `isFibonacci(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` `) ` `or` `isPerfectSquare(` `5` `*` `n` `*` `n ` `-` `4` `)` ` ` `# A utility function to test above functions` `for` `i ` `in` `range` `(` `1` `,` `11` `):` ` ` `if` `(isFibonacci(i) ` `=` `=` `True` `):` ` ` `print` `i,` `"is a Fibonacci Number"` ` ` `else` `:` ` ` `print` `i,` `"is a not Fibonacci Number "` |

**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

Please refer complete article on How to check if a given number is Fibonacci number? for more details!

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