Python/project_euler/problem_07/sol1.py
Christian Clauss 28419cf839 pyupgrade --py37-plus **/*.py (#1654)
* pyupgrade --py37-plus **/*.py

* fixup! Format Python code with psf/black push
2020-01-03 22:25:36 +08:00

55 lines
903 B
Python

"""
By listing the first six prime numbers:
2, 3, 5, 7, 11, and 13
We can see that the 6th prime is 13. What is the Nth prime number?
"""
from math import sqrt
def isprime(n):
if n == 2:
return True
elif n % 2 == 0:
return False
else:
sq = int(sqrt(n)) + 1
for i in range(3, sq, 2):
if n % i == 0:
return False
return True
def solution(n):
"""Returns the n-th prime number.
>>> solution(6)
13
>>> solution(1)
2
>>> solution(3)
5
>>> solution(20)
71
>>> solution(50)
229
>>> solution(100)
541
"""
i = 0
j = 1
while i != n and j < 3:
j += 1
if isprime(j):
i += 1
while i != n:
j += 2
if isprime(j):
i += 1
return j
if __name__ == "__main__":
print(solution(int(input().strip())))