#define ledpin 0
#define timings 1
#define timing_offset 2
//don't forget to change this when adding or removing an led
//          ↓
const int leds[3][3] = {{2, 3, 4}, {4000, 6000, 9000}, {500, 3000, 4500}}; //leds, frequency, duty cycle

int number_of_leds = sizeof(leds[0]) / sizeof(int);
void setup() {
  for (int i = 0; i < number_of_leds; i++) pinMode(leds[ledpin][i], OUTPUT);
}

void loop() {
  for (int i = 0; i < number_of_leds; i++) {
    digitalWrite(leds[ledpin][i], (millis() % leds[timings][i]) <  leds[timing_offset][i]);
  }
}