[Marsman1996]

binomial(n, k) explicitly returns 0 for the out-of-range case k > n, but for k < 0 no branch covers it.

num-integer/src/lib.rs

Lines 1150 to 1154 in 765fd9b

	pub fn binomial<T: Integer + Clone>(mut n: T, k: T) -> T {
	// See http://blog.plover.com/math/choose.html for the idea.
	if k > n {
	return T::zero();
	}

binomial(5i64, -3) == 1
binomial(0i64, -1) == 1

The result is also inconsistent within negative k, depending on how k compares to n:

binomial(5i64, -3)  == 1   // k < 0 && k <= n: silent loop seed
binomial(-3i64, -1) == 0   // k < 0 && k >  n: hits the explicit branch

So this PR mirrors the existing k > n branch for the other end of the range.