Hackerrank "Is Fibo" challenge solution in Python 3
N is a fibonacci number if and only 5N^2 + 4 or 5N^2 – 4 is a perfect square number http://en.wikipedia.org/wiki/Fibonacci_number#Recognizing_Fibonacci_numbers Solution in python 3: import math n = int(input()) for i in range(0,n): number = int(input()) if math.sqrt(5 * number ** 2 + 4).is_integer() or math.sqrt(5 * number ** 2 - 4).is_integer(): print("IsFibo") else: print("IsNotFibo") This solution has a complexity O(1) compared to simple solution by adding all numbers from 0 to N that has a O(n) complexity