void setup() {
  // put your setup code here, to run once:
for(int x=2; x<=13; x++){
  pinMode(x, OUTPUT);
}
}

void loop() {
  // put your main code here, to run repeatedly:
for(int x=2; x<=13; x++){
  digitalWrite(x,HIGH);
  delay(100);
  digitalWrite(x, LOW);
}
for(int x=13; x>=2; x--){
  digitalWrite(x, HIGH);
  delay(100);
  digitalWrite(x, LOW);
}
}