diff --git a/2021/day20.py b/2021/day20.py
new file mode 100644
index 0000000..e9e8afe
--- /dev/null
+++ b/2021/day20.py
@@ -0,0 +1,27 @@
+import numpy as np
+
+def inv_reduce(func, arg, n):
+    for _ in range(n):
+        arg = func(arg)
+        yield arg
+
+
+mapping = {'#':1, '.':0}
+with open('day20input', 'r') as file:
+    rawinput = file.read().strip()
+    cipher_str, _, input_str = rawinput.partition('\n\n')
+    cipher = np.array([mapping[c] for c in cipher_str])
+    input_arr = np.array([[mapping[c] for c in string] for string in input_str.split('\n')])
+
+roll_offsets = [(x,y) for y in [1,0,-1] for x in [1,0,-1]]  # Note roll is opposite direction to our sampling  i.e. (1,1) means (0,0) is old (-1,-1)
+def sample(array):
+    lookup_values = sum([2**(8-n)*np.roll(array, offset, (1,0)) for n,offset in enumerate(roll_offsets)])  # Note axis 1 is x axis 0 is y.
+    return cipher[lookup_values]
+
+def visualize(array):
+    print('\n'.join(''.join(['.','#'][c] for c in row) for row in array))
+
+
+simulated_lights = [t.sum() for t in inv_reduce(sample, np.pad(input_arr, 51), 50)]
+print('Part 1: Lights after 2 enhancements:', simulated_lights[2-1])
+print('Part 2: Lights after 50 enhancements:', simulated_lights[50-1])
diff --git a/2021/day20example b/2021/day20example
new file mode 100644
index 0000000..8fa4bd4
--- /dev/null
+++ b/2021/day20example
@@ -0,0 +1,7 @@
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diff --git a/2021/day20input b/2021/day20input
new file mode 100644
index 0000000..b5b1151
--- /dev/null
+++ b/2021/day20input
@@ -0,0 +1,102 @@
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