int ledpin = 13;

void setup() {
  pinMode(ledpin, OUTPUT);
  randomSeed(analogRead(0));
  int random_r = random(500, 1500);
}

void loop() {
  int i = 0;
  while (i > 10){
  digitalWrite(ledpin, HIGH);
  delay(random_r);
  digitalWrite(ledpin, LOW);
  delay(random_r);
  i = i + 1
  }
}