Data commit

Task/Jacobsthal-numbers/OCaml/jacobsthal-numbers.ocaml

@@ -0,0 +1,27 @@
+let is_prime n =
+  let rec test x =
+    x * x > n || n mod x <> 0 && n mod (x + 2) <> 0 && test (x + 6)
+  in
+  if n < 5
+  then n land 2 <> 0
+  else n land 1 <> 0 && n mod 3 <> 0 && test 5
+
+let seq_jacobsthal =
+  let rec next b a () = Seq.Cons (a, next (a + a + b) b) in
+  next 1
+
+let seq_jacobsthal_oblong =
+  let rec next b a () = Seq.Cons (a * b, next (a + a + b) b) in
+  next 1 0
+
+let () =
+  let show (n, seq, s) =
+    Seq.take n seq
+    |> Seq.fold_left (Printf.sprintf "%s %u") (Printf.sprintf "First %u %s numbers:\n" n s)
+    |> print_endline
+  in
+  List.iter show [
+    30, seq_jacobsthal 0, "Jacobsthal";
+    30, seq_jacobsthal 2, "Jacobsthal-Lucas";
+    20, seq_jacobsthal_oblong, "Jacobsthal oblong";
+    10, Seq.filter is_prime (seq_jacobsthal 0), "Jacobsthal prime"]