A Pythagorean triplet is a set of three numbers [a, b, c], that could represent the length of the sides of a right triangle, so that a**2 + b**2 == c**2. We will agree to always write the triplets with a <= b <= c, and we will only consider positive integer-lengthed sides. Write the function pythag(p) which finds a Pythagorean triplet with perimeter p (the perimeter is a+b+c) or returns False if there is no such triplet.