Copy this into Arduino IDE.
int a1 = 13;
int a10 = 12;
int a100 = 11;
void setup() {
pinMode(a1, OUTPUT);
pinMode(a10, OUTPUT);
pinMode(a100, OUTPUT);
}
void loop() {
digitalWrite(a1, HIGH);
delay(1000);
digitalWrite(a1, LOW);
digitalWrite(a10, HIGH);
delay(1000);
digitalWrite(a10, LOW);
digitalWrite(a100, HIGH);
delay(1000);
digitalWrite(a100, LOW);
delay(1000);
}