T binomial(T)(in T n, T k) pure nothrow {
    if (k > (n / 2))
        k = n - k;
    T bc = 1;
    foreach (T i; T(2) .. k + 1)
        bc = (bc * (n - k + i)) / i;
    return bc;
}

void main() {
    import std.stdio, std.bigint;

    foreach (const d; [[5, 3], [100, 2], [100, 98]])
        writefln("(%3d %3d) = %s", d[0], d[1], binomial(d[0], d[1]));
    writeln("(100  50) = ", binomial(100.BigInt, 50.BigInt));
}