int ledler[] = {2,3,4,5,6,7};

void setup() {

  for(int i=0; i<6; i++){
    
  pinMode(ledler[i], OUTPUT);
  
  }

}

void loop() {

  for(int i=0; i<6; i++){
    digitalWrite(ledler[i], HIGH);
    delay(100);
    digitalWrite(ledler[i], LOW);
  }

  for(int j=5; j>-1; j--){
    digitalWrite(ledler[j], HIGH);
    delay(100);
    digitalWrite(ledler[j], LOW);
  }

}