struct LEDType {
  unsigned long LastMillis = 0;
  unsigned long interval   = 500;
  boolean       isOn = false;
  int           Pin;
};

const int NoOfLEDs = 2;

LEDType LED[NoOfLEDs];

void SetLED(int No, int State) {
  LED[No].isOn = State;
  digitalWrite(LED[No].Pin, LED[No].isOn);
}


void BlinkLedNo(int No) {
    if (millis() - LED[No].LastMillis > LED[No].interval) {
      LED[No].LastMillis = millis();
      LED[No].isOn = !LED[No].isOn;
      SetLED(No, LED[No].isOn);
    }
}

void BlinkLeds() {
  for (int i = 0; i < NoOfLEDs; i++ ) BlinkLedNo(i);
}

void setup() {
  Serial.begin(115200);
  // Just a quick initialization
  for (int i = 0; i < NoOfLEDs; i++ ) {
    LED[i].interval = 300 * (i + 1);  // Interval for 0 -> 300 msec, for 1 -> 600 msec
    LED[i].Pin = 9 + i; // Only valid for max. 5 Led, as 9 + 4 = 13 (Pin 13)
    pinMode(LED[i].Pin, OUTPUT);
  }
  SetLED(0,LOW);
  SetLED(1,LOW);

}

void loop() {
  BlinkLeds();
}