int delay_on = 300, delay_off = 100;
int led_red = 13, led_green = 12, led_blue = 11;
int leds[3] = {13, 12, 11};
int total_leds = sizeof(leds) / sizeof(leds[0]);

void setup() {
  pinMode(leds[0], OUTPUT);
  pinMode(leds[1], OUTPUT);
  pinMode(leds[2], OUTPUT);
}

void loop() {
  practice_3();
}

void practice_3() {
  int wait_on = 500;

  turn_led(led_red, wait_on, wait_on); // led rojo
  turn_led(led_green, wait_on, wait_on); // led verde
  turn_led(led_blue, wait_on, wait_on); // led azul

  turn_two_leds(led_red, led_green, wait_on, wait_on); // leds rojo y verde
  turn_two_leds(led_green, led_blue, wait_on, wait_on); // leds verde y azul
  turn_two_leds(led_blue, led_red, wait_on, wait_on); // leds azul y rojo
}

void turn_led(int led, int wait_on, int wait_off) {
  digitalWrite(led, HIGH);
  delay(wait_on);
  digitalWrite(led, LOW);
  delay(wait_off);
}

void turn_two_leds(int led_1, int led_2, int wait_on, int wait_off) {
  digitalWrite(led_1, HIGH);
  digitalWrite(led_2, HIGH);
  delay(wait_on);
  digitalWrite(led_1, LOW);
  digitalWrite(led_2, LOW);
  delay(wait_off);
}

void practice_2() {
  for (int i = 0; i < total_leds; i++) {
    turn_led(leds[i], delay_on, delay_off);
  }
}