int ledPin[] = {13, 12, 11,10};
int ledDelay[4]={8000, 4000,2000, 1000};
// declare other required variables
unsigned long lastChangeTime[4];  
int ledState[4];                  
unsigned long currTime;

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


void loop() {
  // implement the toggling logic
  currTime = millis();
  for (int i = 0; i < 4; i++) {
    if (currTime - lastChangeTime[i] >= ledDelay[i]) {
       ledState[i] = !ledState[i]; 
      digitalWrite(ledPin[i], ledState[i]);
      lastChangeTime[i] = currTime;
    }
  }
}