int DT=500;
void setup() {
for(int x=2;x<=9;x++){
pinMode(x,OUTPUT);
digitalWrite(x,HIGH);
}
}
void loop() {
if(DT<=0){
DT=500;
}

for(int i=2;i<=9;i++){
digitalWrite(i,LOW);
delay(DT);
digitalWrite(i,HIGH);
delay(DT);

}
for(int i=9;i--;){
digitalWrite(i,LOW);
delay(DT);
digitalWrite(i,HIGH);
delay(DT);
}
DT=DT/2;
}