int pinCount= 6;
int pins[]={4,16,17,5,18,19};
// #define LED 25
//........#define LED 13
void setup() {
pinMode(4,OUTPUT);
pinMode(16,OUTPUT);
pinMode(17,OUTPUT);
pinMode(5,OUTPUT);
pinMode(18,OUTPUT);
pinMode(19,OUTPUT);
}


void loop() {
   for(int i=0,j=5;i<3,j>2;i++,j--){
    digitalWrite(pins[i],HIGH);
    digitalWrite(pins[j],HIGH);
    delay(30);
    digitalWrite(pins[i],LOW);
    digitalWrite(pins[j],LOW);
    delay(100);
   }
   for(int i=2,j=3;i>=0,j<=5;i--,j++){
    digitalWrite(pins[i],HIGH);
    digitalWrite(pins[j],HIGH);
    delay(30);
    digitalWrite(pins[i],LOW);
    digitalWrite(pins[j],LOW);
    delay(100);
   }
}