void print64(uint64_t t) {

  char buffer[21] = "                    ";
  for(int i=19; i>=0 && t!=0ULL; i--) {
    buffer[i] = '0' + (t % 10);
    t /= 10;
  }

  String a = buffer;
  a.replace(" ", "");
  if (a == "") a = "0";

  Serial.println(a);
}

void setup() {
  Serial.begin(115200);

  // Max uint64_t : 18446744073709551615
  uint64_t n = -200;

  while (n > 200 or n < 200) {
    n++;
    print64(n);
  }
}

void loop() {}