diff --git a/2021/day6/day6.py b/2021/day6/day6.py
new file mode 100755
index 0000000..cd62018
--- /dev/null
+++ b/2021/day6/day6.py
@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+import sys
+import functools
+
+@functools.cache
+def spawns(days):
+    acc = days//7
+    days -= 9
+    acc += sum(spawns(days-x*7) for x in range(days//7))
+    return acc
+
+if __name__ == '__main__':
+    inp = [int(i) for i in sys.stdin.readline().split(',')]
+
+    def do(days):
+        spawns.cache_clear()
+        return sum(1 + spawns(days + (6 - fish)) for fish in inp)
+    print(do(80))
+    print(do(256))