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);
  }
}