gistfile1.ml

let rev = List.fold_left (fun a x -> x::a) [];;

let is_prime x = 
	let rec pom a =
		if a*a > x then true
		else
			if x mod a = 0 then false
			else pom (a+2)
	in if x mod 2 = 0 then false
	else pom 3;;

let next_ltps base ten =
	List.fold_left 
		(fun a x -> 
			(List.fold_left (fun acc base ->
			let ltp = ten*x + base in if is_prime ltp then ltp::acc else acc)
			[] (rev base))@a
			)
		[]
		[1;2;3;4;5;6;7;8;9];;

let make_tens n =
	let rec pom a prev n =
		if n = 0 then a
		else pom (prev::a) (prev*10) (n-1)
	in rev (pom [] 10 n);;
		
let ltp =
	List.fold_left 
	(fun (acc, prev) ten -> let a = next_ltps prev ten in
							(a@acc, a)
	)
	([7;5;3;2],[7;5;3])
	(make_tens 8);;

let ltp n = 
	let rec pom l n = 
		match l with
		| (h::tl) -> if n = 0 then h
					 else pom tl (n-1)
		| [] -> assert false		
	and fst (a, _) = a 
	in pom (rev (fst ltp)) (n - 1);;

let n = read_int () in	
	print_int (ltp n);;