void setup() {
  for (int i = 0; i <= 13; i++) {
    pinMode(i, OUTPUT);
  }
}

void loop() {
  // Start with center to outside
  for (int i = 0; i <= 6; i++) {
    int left = 6 - i;
    int right = 7 + i;
    digitalWrite(left, HIGH);
    digitalWrite(right, HIGH);
    delay(150);
    digitalWrite(left, LOW);
    digitalWrite(right, LOW);
    delay(150);
  }

  // Left to right
  for (int i = 0; i <= 13; i++) {
    digitalWrite(i, HIGH);
    delay(100);
    digitalWrite(i, LOW);
    delay(100);
  }

  // Right to left
  for (int i = 13; i >= 0; i--) {
    digitalWrite(i, HIGH);
    delay(100);
    digitalWrite(i, LOW);
    delay(100);
  }

  // Blink all LEDs once
  for (int i = 0; i <= 13; i++) {
    digitalWrite(i, HIGH);
  }
  delay(200);
  for (int i = 0; i <= 13; i++) {
    digitalWrite(i, LOW);
  }
  delay(200);

  // End with center to outside
  for (int i = 0; i <= 6; i++) {
    int left = 6 - i;
    int right = 7 + i;
    digitalWrite(left, HIGH);
    digitalWrite(right, HIGH);
    delay(150);
    digitalWrite(left, LOW);
    digitalWrite(right, LOW);
    delay(150);
  }
}