An integer n is called a square if n = m*m for some integer m. As we all know, 1, 4, 9, 16, and 25 are squares. But what about bigger numbers, like 543168? (It's not a square. 543169 is.) Write a function, is_square that takes as argument a positive integer and return True if that integer is the square of another integer, and False if it is not.