FACTDOUBLE(n)

The FACTDOUBLE function calculates the double factorial of a number n. It takes into account whether n is even or odd, and then carries out a factorial calculation using either the even or the odd numbers up to n.

For example:

FACTDOUBLE(5)  returns 15, that is 5 * 3 * 1.

FACTDOUBLE(6)  returns 48, that is 6 * 4 * 2.

FACTDOUBLE also works with fractional numbers (see FACT). For example:

FACTDOUBLE(5.5)  returns 28.875, that is 5.5 * 3.5 * 1.5.

FACTDOUBLE(6.5)  returns 73.125, that is 6.5 x 4.5 x 2.5.

See also:

Other mathematical functions