const int pins[] = {2, 3, 4};

void setup() {
  // put your setup code here, to run once:
  for (int i = 0; i < 3; i++)
    pinMode(pins[i], OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  for (int i = 0; i < 3; i++)
    digitalWrite(pins[i], HIGH);

  delay(2500);
  
  for (int i = 0; i < 3; i++)
    digitalWrite(pins[i], LOW);
}