MODULE Primes;

  CONST
    N = 20 (*252*);   
    M = 16; (* M ~ sqrt(N) *)
    LL = 10; (* no. of primes placed on a line *)

  VAR
    i, k, x : CARDINAL;
    inc, lim, square, L : CARDINAL;
    prime : BOOLEAN;
    P, V : ARRAY[0..M] OF CARDINAL;
    r, c : CARDINAL;

BEGIN
  x := 1; inc := 4; lim := 1; square := 9;
  FOR i := 3 TO N DO
    (* find next prime number p[i] *)
    r := 0;
    REPEAT
      INC(r);
      x := x + inc; inc := 6 - inc;
      IF square <= x
	THEN
	  lim := lim + 1; V[lim] := square;
	  square := P[lim+1] * P[lim+1];
      END; (* IF *)
      k := 2; prime := TRUE;
      c := 0;
      WHILE prime & (k < lim) DO
	INC(c);
	k := k + 1;
	IF V[k] < x
	  THEN
	    V[k] := V[k] + 2 * P[k];
	END; (* IF *)
        prime := x # V[k];
      END; (* WHILE *)
    UNTIL prime;
    IF i <= M
      THEN
	P[i] := x;
    END; (* IF *)
    WRITE(x); L := L + 1;
    IF L = LL
      THEN
	WRITELN; L := 0;
    END; (* IF *)
  END; (* FOR *)
END Primes.