int testedNumber = 19;
int i;
int result;
int prime;

void setup() {

  Serial.begin(9600);
  Serial.println("BEGIN");
  Serial.println();

}

void loop() {

  for (i = 2; i < (testedNumber/2); i++) {
    result = testedNumber / i;
    if (testedNumber % result == 0) {
      prime = 0;
      break;
    }
    prime = 1;
  }
  
  if (prime !=0) {
    Serial.print(testedNumber);
    Serial.println(" is prime");
  }

  testedNumber++;
} // loop end