int ledPin[] = {13, 12, 11, 10}; 
int ledDelay[] = {8000, 4000, 2000, 1000}; 
unsigned long previousMillis[4] = {0, 0, 0, 0};  
bool ledState[] = {LOW, LOW, LOW, LOW};   

void setup() {
  for (int i = 0; i < 4; i++) {
    // Set LED pins as OUTPUT
    pinMode(ledPin[i], OUTPUT);  
    // Initialize LEDs to LOW   
    digitalWrite(ledPin[i], LOW);    
  }
}

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

  for (int i = 0; i < 4; i++) {
    if (currentMillis - previousMillis[i] >= ledDelay[i]) {
      previousMillis[i] = currentMillis;
      ledState[i] = !ledState[i];
      digitalWrite(ledPin[i], ledState[i]);
    }
  }
}