Here's the SQL factorial:

With Fact (Num, Factorial)

As

(

Select 0 as Num, convert(bigint, 1) as Factorial

Union All

Select Num + 1, convert(bigint, Num + 1) * Factorial from Fact

Where Num + 1 <= 20 --Recursion Buster; not really necessary since Fact(21) doesn't fit in a BigInt anyway

)

Select * from Fact