#define LED1 PA0
#define LED2 PA1
#define LED3 PA2
#define LED4 PA3

int leds[] = {LED1, LED2, LED3, LED4};
void setup()
{
   for (int i = 0; i < 4; i++)
    {
        pinMode(leds[i], OUTPUT);
    }
}

void loop()
{
   for (int number = 0; number < 16; number++)
    {
        for (int i = 0; i < 4; i++)
        {
            if (number & (1 << i))
            {
                digitalWrite(leds[i], HIGH);
            }
            else
            {
                digitalWrite(leds[i], LOW);
            }
        }

        delay(500);
    }
}