let rec arr_exists p arr b e =
   if b >= e
      then false
      else if p arr.(b)
         then true
         else arr_exists p arr (b + 1) e

let n_primes n =
   let rec gather c x ps =
      if c == n
         then ps
         else if arr_exists (fun y -> x mod y = 0) ps 0 c
            then gather c (x + 2) ps
            else (ps.(c) <- x; gather (c + 1) (x + 2) ps)
   in gather 1 5 (Array.make n 2) ;;

print_int (n_primes 100000).(99999)