void setup() {
  pinMode(2,OUTPUT);
  pinMode(4,OUTPUT);
  pinMode(16,OUTPUT);
  pinMode(17,OUTPUT);
  pinMode(5,OUTPUT);
  pinMode(18,OUTPUT);
  pinMode(19,OUTPUT);
  pinMode(21,OUTPUT);
  

}

void loop() {
  digitalWrite(2,LOW);
  delay(500);
  digitalWrite(4,HIGH);
  delay(500);
  digitalWrite(16,LOW);
  delay(500);
  digitalWrite(17,HIGH);
  delay(500);
  digitalWrite(5,LOW);
  delay(500);
  digitalWrite(18,HIGH);
  delay(500);
  digitalWrite(19,LOW);
  delay(500);
  digitalWrite(21,HIGH);
  delay(500);
}