diff --git a/0020.py b/0020.py
new file mode 100644
index 0000000..4c1228d
--- /dev/null
+++ b/0020.py
@@ -0,0 +1,12 @@
+from functools import reduce
+
+import util
+
+target = 648
+
+result = util.factorial(100)
+
+digits_sum = reduce(lambda x, y: x + y, map(lambda x: int(x), list(str(result))))
+
+print(digits_sum)
+print(digits_sum == target)
diff --git a/util.py b/util.py
index 68acf27..6c63983 100644
--- a/util.py
+++ b/util.py
@@ -1,3 +1,5 @@
+from functools import reduce
+
 def find_largest_prime_factor(n):
     prime_factor = 1
     factors.append(prime_factor)
@@ -34,3 +36,6 @@ def find_prime_factors(n):
     factors.append(n)
 
     return factors
+
+def factorial(n):
+    return reduce(lambda x, y: x * y, range(1, n + 1))