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

unsigned long lastChangeTime[4];
unsigned long currTime;
void setup() {
  currTime = millis();
  for(int i=0;i<4;i++){
    lastChangeTime[i] = currTime;  
    pinMode(ledPin[i], OUTPUT);
  }
  Serial.begin(9600);
}
void loop() {
  currTime = millis();
  for (int i = 0; i < 4; i++) {
    if (currTime - lastChangeTime[i] >= ledDelay[i]) {
      digitalWrite(ledPin[i], !digitalRead(ledPin[i]));
      Serial.print("Current time: ");
      Serial.print(currTime);
      Serial.print(" ms, Last change time for LED on pin ");
      Serial.print(ledPin[i]);
      Serial.print(": ");
      Serial.print(lastChangeTime[i]);
      Serial.println(" ms");
      lastChangeTime[i] = currTime;
    }
  }
}