const int ledPin[] = { 2, 3, 4, 5, 6, 7, 8, 9 };
const int numPins = sizeof(ledPin) / sizeof(ledPin[0]);
const int numStates = numPins / 2;

const unsigned long interval = 1000;
unsigned long previousTime;
int state;

void setup()
{
  for ( int i = 0; i < numPins; ++i ) {
    pinMode(ledPin[i], OUTPUT);
    digitalWrite(ledPin[i], LOW );
  }
  digitalWrite(ledPin[0], HIGH );
  digitalWrite(ledPin[1], HIGH );
}

void loop() {

  unsigned long currentMillis = millis();

  if (currentMillis - previousTime >= interval) {
    previousTime = currentMillis;
    digitalWrite(ledPin[state*2], LOW);
    digitalWrite(ledPin[state*2+1], LOW);
    state++;
    if ( state >= numStates ) {
      state = 0;
    }
    digitalWrite(ledPin[state*2], HIGH);
    digitalWrite(ledPin[state*2+1], HIGH);
  }
}