1 files changed, 53 insertions, 0 deletions
diff --git a/challenge-147/roger-bell-west/python/ch-1.py b/challenge-147/roger-bell-west/python/ch-1.py
new file mode 100755
index 0000000000..18f827e01c
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+++ b/challenge-147/roger-bell-west/python/ch-1.py
@@ -0,0 +1,53 @@
+#! /usr/bin/python3
+
+import unittest
+
+from math import sqrt,floor
+from collections import deque
+
+def genprimes(mx):
+  primesh=set(range(2,4))
+  for i in range(6,mx+2,6):
+    for j in range(i-1,i+2,2):
+      if j <= mx:
+        primesh.add(j)
+  q=deque([2,3,5,7])
+  p=q.popleft()
+  mr=floor(sqrt(mx))
+  while p <= mr:
+    if p in primesh:
+      for i in range(p*p,mx+1,p):
+        primesh.discard(i)
+    if len(q) < 2:
+      q.append(q[-1]+4)
+      q.append(q[-1]+2)
+    p=q.popleft()
+  primes=list(primesh)
+  primes.sort()
+  return primes
+
+def ltruncprimes(count):
+  out=[]
+  lt=0
+  p=[str(i) for i in genprimes(500)]
+  pp=set(p)
+  for pc in p:
+    l=len(pc)
+    c=True
+    for i in range(1,l):
+      if not pc[i:l] in pp:
+        c=False
+        break
+    if c:
+      out.append(int(pc))
+      lt += 1
+      if lt >= count:
+        break
+  return out
+
+class TestLtruncprimes(unittest.TestCase):
+
+        def test_ex1(self):
+          self.assertEqual(ltruncprimes(20),[2, 3, 5, 7, 13, 17, 23, 37, 43, 47, 53, 67, 73, 83, 97, 113, 137, 167, 173, 197],'example 1')
+
+unittest.main()