void setup() {
  // put your setup code here, to run once:
  for (int i=2; i<10; i++) { 
    pinMode(i, OUTPUT); 
  }
}

void allLEDsOff(void) {
  for (int i=2; i<10; i++) { 
   digitalWrite(i, LOW); 
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  for (int i=2; i<9; i++) {
    allLEDsOff();
    digitalWrite(i, HIGH);
delay(200);
  }
  for (int i=9; i>2; i--) {
    allLEDsOff();
    digitalWrite(i, HIGH);
    delay(200);
  }
}