.divide(BigIntegerMath.factorial(n - k));
        assertEquals(expected, BigIntegerMath.binomial(n, k));
      }
    }
  }

  public void testBinomialOutside() {
    for (int i = 0; i <= 50; i++) {
      int n = i;
      assertThrows(IllegalArgumentException.class, () -> BigIntegerMath.binomial(n, -1));