int ledPin[] = {13, 12, 11, 10};
int ledDelay[4] = {8000, 4000, 2000, 1000};

unsigned long lastChangeTimes[4] = {0, 0, 0, 0};
bool ledState[4] = {LOW, LOW, LOW, LOW};

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(ledPin[i], OUTPUT);
    digitalWrite(ledPin[i], ledState[i]);
    
    lastChangeTimes[i] = millis();
  }
}

void loop() {
  unsigned long currTime = millis();

  for (int i = 0; i < 4; i++) {
    if (currTime - lastChangeTimes[i] >= ledDelay[i]) {

      ledState[i] = !ledState[i];
      digitalWrite(ledPin[i], ledState[i]);
      
      lastChangeTimes[i] = currTime;
    }
  }
}