int ackermann(int m, int n) {
  if (m == 0)
    return n + 1;
  else if (m > 0 && n == 0)
    return ackermann(m - 1, 1);
  else
    return ackermann( m - 1, ackermann(m, n - 1) );
}

// Call function to produce output:
// the first 4x7 Ackermann numbers
void setup() {
  for (int m=0; m<4; m++) {
    for (int n=0; n<7; n++) {
      print(ackermann(m, n), " ");
    }
    println();
  }
}