const int numLeds = 4;          
const int ledPins[numLeds] = {2, 3, 4, 5};  
void setup() {
    for (int i = 0; i < numLeds; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}
void loop() {
  
  for (int i = 0; i < (1 << numLeds); i++) {
    for (int j = 0; j < numLeds; j++) {
      if ((i >> j) & 1) {
        digitalWrite(ledPins[j], HIGH); 
      } else {
        digitalWrite(ledPins[j], LOW);   
      }
    }
    delay(500);  }
}
//The following pattern is just coutning in binary number system