int led1_3=2;
int led2_4=15;

void setup() {
  // put your setup code here, to run once:
  pinMode(led1_3, OUTPUT);
  pinMode(led2_4, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  for(int i=0; i<=10000; i = i+30)
  {
    digitalWrite(led1_3, HIGH);
    delay(i);
    digitalWrite(led1_3, LOW);
    delay(i);
    digitalWrite(led2_4, HIGH);
    delay(i);
    digitalWrite(led2_4, LOW);
    delay(i);
  }
}