// Blink a led 10 times with 150ms and then stay off for 10 times.

const int ledPin = LED_BUILTIN;

unsigned long previousMillis;
int count;
bool blink;

void setup()
{
  pinMode( ledPin, OUTPUT);
}

void loop()
{
  unsigned long currentMillis = millis();

  if( currentMillis - previousMillis >= 150)
  {
    previousMillis = currentMillis;

    if( count < 10)   // even number to turn led off during longer interval
    {
      blink = !blink;
      digitalWrite( ledPin, blink ? HIGH : LOW);  // turn bool variable into HIGH and LOW
    }

    count++;
    if( count > 20)
      count = 0;      // reset the variable
  }
}