Arduino Christmas Lights

const int led_count = 12; // Number of leds
const int led_delay = 150; // A delay constant
const int led_pins[led_count] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}; // Pins of the leds

void off() {        // All leds off
  for (int i = 0; i <= led_count; i++) {
    digitalWrite(led_pins[i], LOW);
  }
  delay(led_delay * 5);
}

void basic() {      // Basic animation
  for (int j = 0; j <= led_count; j++) {
    digitalWrite(led_pins[j], HIGH);
    delay(led_delay);
  }
  off();
}

void chaser() {     // Chaser animation
  for (int j = 0; j <= led_count; j++) {
    digitalWrite(led_pins[j], HIGH);
    delay(led_delay);
    digitalWrite(led_pins[j-1], LOW);
    delay(led_delay);
  }
  off();
}

void pairs() {      // Pairs animation
  for (int j = 0; j <= led_count; j++) {
    digitalWrite(led_pins[j], HIGH);
    digitalWrite(led_pins[j + 2], HIGH);
    delay(led_delay * 1.5);
    digitalWrite(led_pins[j], LOW);
    digitalWrite(led_pins[j + 2], LOW);
  }
  off();
}

void randoms() {    // Random leds animation
  for (int o = 0; o <= 50; o++) {
    int r = random(1,12);
    digitalWrite(led_pins[r], HIGH);
    delay(led_delay);
    digitalWrite(led_pins[r], LOW);
  }
  off();
}

void setup() {
  for (int i = 0; i <= led_count - 1; i++) {        // Initializing the pins
    pinMode(led_pins[i], OUTPUT);
  }
  off();
}

void loop() {
  basic();
  chaser();
  pairs();
  randoms();
  delay(1000);
}