MULTINOMIAL function
Description
MULTINOMIAL(a1[,a2, ... , an]) returns the factorial of the sum of values divided by the product of the values' factorials.
$$ \mathrm{multinomial}(a_1,a_2, ..., a_n) = \frac{(a_1+a_2+ ... +a_n)!}{a_1! a_2! ... a_n!} $$
If any argument is not an integer, it is truncated.
If any argument is negative, the program returns an error.