int i;

void setup() {

  Serial.begin(9600);
  
  // We'll want to count down in setup so that it
  // only runs once
  for ( i = 30; i >= 0; i-- ) {
    Serial.println(i);
  }
}

void loop() {
  // Do nothing in loop()
}

Simulator: https://tinkercad.com/things/am0QKi7DmoI