Add a list-cached version of problem 044 (#5)

euler0XX/euler044-list.py

@@ -0,0 +1,21 @@
+from itertools import count
+from math import sqrt
+
+def is_pentagonal(number):
+    n = (1 + sqrt(1 + 24 * number)) / 6
+    return n.is_integer()
+
+prev = []
+for i in count(1):
+    pk = i * (3 * i - 1) // 2
+
+    for pj in prev:
+        if is_pentagonal(pk + pj) and is_pentagonal(pk - pj):
+            print(pk - pj)
+            break
+
+    else:
+        prev.append(pk)
+        continue
+
+    break