const int LED_Pins[4] = {0, 4, 9, 13};  // Pins connected to the LEDs

void setup() {
  // Set LED pins as OUTPUT
    for (int i = 0; i < 4; i++) {
        pinMode(LED_Pins[i], OUTPUT);
          }
          }

          void loop() {
            // Count from 1 to 15 in increasing order
              for (int number = 1; number <= 15; number++) {
                  displayBinary(number);
                      delay(1000);  // Delay 1 second
                        }

                          // Wait for 2 seconds after reaching 15
                            delay(2000);

                              // Count from 14 down to 1 in decreasing order
                                for (int number = 14; number >= 1; number--) {
                                    displayBinary(number);
                                        delay(1000);  // Delay 1 second
                                          }

                                            // Wait for 2 seconds after reaching 1
                                              delay(2000);
                                              }

                                              // Function to display a decimal number in binary on LEDs
                                              void displayBinary(int num) {
                                                for (int i = 0; i < 4; i++) {
                                                    digitalWrite(LED_Pins[i], (num >> (3 - i)) & 1);
                                                      }
                                                      }