diff --git a/archive/o/ocaml/prime-number.ml b/archive/o/ocaml/prime-number.ml
new file mode 100644
index 000000000..dba372cd3
--- /dev/null
+++ b/archive/o/ocaml/prime-number.ml
@@ -0,0 +1,18 @@
+let has_odd_divisor_under_sqrt n =
+  let rec aux k = k <= n / k && (n mod k = 0 || aux (k + 2)) in
+  aux 3 (* Assumes n > 3. All other cases will be caught elsewhere *)
+
+let prime = function
+  | 0 | 1 -> false
+  | 2 | 3 -> true
+  | n when n mod 2 = 0 -> false
+  | n -> not (has_odd_divisor_under_sqrt n)
+
+let parse_args argv =
+  match argv with [| _; n |] -> int_of_string_opt n | _ -> None
+
+let () =
+  print_endline
+    (match parse_args Sys.argv with
+    | Some num when num >= 0 -> if prime num then "Prime" else "Composite"
+    | _ -> "Usage: please input a non-negative integer")