int a;
int b;

void setup() {
  Serial.begin(9600);
}
void loop() {
  randomSeed(analogRead(A0));
  a = random(1, 20);
  b = random(1, 20);
  while (a == b)  {
    b = random(1, 20);
  }
  Serial.print(a); Serial.print(" und ");
  Serial.println(b);
  delay(1000);
}