int ledPins[] = {2, 3, 4, 5, 6, 7};

void setup() {
  // put your setup code here, to run once:
for (int i = 0; i < 7;i++)
{
 pinMode(ledPins[i], OUTPUT); 
}
}
void loop() {
  // put your main code here, to run repeatedly:
  for (int i = 0; i < 7;i++)
{
  digitalWrite(ledPins[i], HIGH);
  delay(400);
  digitalWrite(ledPins[i], LOW);
  delay(400);
  digitalWrite(ledPins[i], HIGH);
  delay(400);
  digitalWrite(ledPins[i], LOW);
}
}