python code to find primes

1 files changed, 15 insertions, 0 deletions

diff --git a/challenge-172/walt-mankowski/python/primes.py b/challenge-172/walt-mankowski/python/primes.py
new file mode 100644
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+++ b/challenge-172/walt-mankowski/python/primes.py
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+from math import sqrt
+
+# find the primes up to n using the sieve of Eratosthenes and return
+# them as list
+def primes_to(n):
+    is_prime = [True] * (n+1)
+    is_prime[0] = is_prime[1] = False
+    for i in range(2, int(sqrt(n))+1):
+        if is_prime[i]:
+            for j in range(i+i, n+1, i):
+                is_prime[j] = False
+
+    return [i for i,val in enumerate(is_prime) if val]
+
+