diff --git a/17.9.py b/17.9.py
new file mode 100644
index 0000000..c442b14
--- /dev/null
+++ b/17.9.py
@@ -0,0 +1,31 @@
+def decorator(maximum):
+    cache = [None for _ in range(maximum)]
+
+    def _decorator(func):
+
+        def __decorator(arg: int, **kw):
+            if arg > maximum:
+                return f'Out of range ({arg})'
+
+            if cache[arg-1] != None:
+                return f'Already in cache: {cache[arg-1]}'
+            else:
+                y = func(arg, **kw)
+                cache[arg-1] = y
+                return y
+            
+        return __decorator
+    
+    return _decorator
+
+
+@ decorator(10)
+def fib(n, f0=1, f1=1, count=1):
+    if count < n:
+        return fib(n, f0=f1, f1=f0+f1, count=count+1)
+    return f1
+
+if __name__ == '__main__':
+    print(fib(5))
+    print(fib(5))
+    print(fib(11))
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