3 LEDs, different speed

const uint8_t LED_PIN[3] = { 25, 26, 27 };         // GPIO pins LED
const uint16_t INTERVAL[3] = { 3131, 1117, 200 };  // interval millisec

void setup() {
  for (uint8_t i = 0; i < 3; i++) pinMode(LED_PIN[i], OUTPUT);
}

void loop() {
  for (uint8_t i = 0; i < 3; i++) digitalWrite(LED_PIN[i], millis() % INTERVAL[i] * 2 < INTERVAL[i] ? HIGH : LOW);
}