byte leds[]={2,3,4,5,6,7};
void setup() {
  // put your setp code here, to run once:
  for(byte i=0; i<6; i++)
  {
    pinMode(leds[i], OUTPUT);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  for(byte x=0; x<6; x++)
  {
    digitalWrite(leds[x], HIGH);
    delay(100);
    digitalWrite(leds[x], LOW);
    delay(100);
  }

  for(byte y=6; y>0; y--)
  {
    digitalWrite(leds[y], HIGH);
    delay(100);
    digitalWrite(leds[y], LOW);
    delay(100);
  }
}