import math
def get_prime_factor(number):
result = []
if number < 2:
return result
while number % 2 == 0:
result.append('2')
number /= 2
for i in range (3, int(math.sqrt(number)) + 1, 2):
if number % i == 0:
result.append(str(i))
number /= i
if number > 2:
result.append(str(int(number)))
return result
def testPrimeFactor():
assert len(get_prime_factor(-1)) == 0
assert "2x2x3" == 'x'.join(get_prime_factor(12))
assert "2x2x5x5" == 'x'.join(get_prime_factor(100))
assert "67x337x2797x14251" == 'x'.join(get_prime_factor(900000001213))
if __name__ == '__main__':
testPrimeFactor()