int LED[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, A0, A1, A2, A3, A4, A5};
int i;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  for (i = 0; i < 18; i++) {
    pinMode(LED[i], OUTPUT);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  for (i = 0; i < 18; i++ ) {
    digitalWrite(LED[i], HIGH);
    delay(50);
    digitalWrite(LED[i], LOW);
  }
}