Here is the code we wrote today:

public int factorial(int n) {
  if(n == 0) {
    return 1;
  }

  return n * factorial(n-1);
}

public int bunnyEars(int bunnies) {
  if(bunnies == 0) {
    return 0;
  }
  return bunnyEars(bunnies-1)+2;
}

public int bunnyEars2(int bunnies) {
  if(bunnies == 0) {
    return 0;
  }
  
  if(bunnies % 2 == 0) {
    return bunnyEars2(bunnies-1) + 3;
  }
  return bunnyEars2(bunnies-1) + 2;
  //return bunnyEars2(bunnies-1) + 2 + ((bunnies-1) % 2);
}

public int triangle(int rows) {
  if(rows == 0) {
    return 0;
  }
  
  return triangle(rows-1) + rows;
}