void setup() {
  // array of GPIO pins
  int ledPins[] = {15, 2, 4, 5};
  int numLeds = 4;

  // Initialize each GPIO pin as an output and turn on the LED
  for (int i = 0; i < numLeds; i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], HIGH);
    delay(500);
  }
}

void loop() {
  // No code needed in the loop for this example
}