Hey,
try using the modulo (%) to check the value you're at.
If the modulo = 0, then it means that you're at a specific value and that you want to run something special.
Copy paste the code below, and look oat the output window.
I just used random numbers, change it for yours.

-------------------------
void setup() {
 size(200,200);
 background(0);
 noLoop();
}

void draw() {
for (int i=0; i<14; i++) {
 if (i%5 == 0) {
   println("Do something special");
 }
 else {
  println("Do something");
 }
}
}

-------------------------

Cheers
Steven