void setup()
{
  Serial.begin(115200);
  pinMode(23, OUTPUT);
  pinMode(19, OUTPUT);
  pinMode(18, OUTPUT);
}

void loop() 
{
  // on for 3 LEDs
  Serial.println("Turning On 3 LEDs...");
  digitalWrite(18, LOW);
  digitalWrite(19, LOW);
  digitalWrite(23, LOW);
  // Delay 2 seconds
  delay(2000);
  // OFF for 3 LEDs
  Serial.println("Turning OFF 3 LEDs...");
  digitalWrite(18, HIGH);
  digitalWrite(19, HIGH);
  digitalWrite(23, HIGH);
  // delay 3 seconds
  delay(3000);
}