(* 目的：問題に与えられた漸化式の一般項を求める *) 
(* a : int -> int *) 
let rec a n = 
  if n = 0 then 3 
           else 2 * a (n - 1) - 1 
 
(* テスト *) 
let test1 = a 0 = 3 
let test2 = a 1 = 5 
let test3 = a 2 = 9 
let test4 = a 3 = 17 
let test5 = a 4 = 33