分解质因数

例如：输入6，输出 2*3=6

def prime_factor():
    n = int(input())
    old_n = n
    nums = []
    while n > 1:
        for i in range(2, n+1):
            if n % i == 0:
                n //= i
                nums.append(str(i))
                break
    res = '*'.join(nums) + '=' + str(old_n)
    print(res)