```
class Solution(object):
def getPermutation(self, n, k):
"""
:type n: int
:type k: int
:rtype: str
"""
ans = ""
rec = set()
for i in xrange(1, n + 1): rec.add(i)
pos = n - 1
while rec:
cur = 0
for i in rec:
if k - math.factorial(pos) > 0:
k -= math.factorial(pos)
else:
ans += str(i)
rec.remove(i)
pos -= 1
break
return ans
```