Necromancer math

[Asteron]

We are playing a 3.P game and one of my friends is joining the game as a necromancer. However, I've never DMed a necromancer before and I'm a little fuzzy on the math for creating undead. According to the normal rules, you can create undead at rate of twice your HD. That number is doubled by desecrate.

Do you use normal D&D math for multipliers?

I.E:
9 levels(2+(2-1))=27 hd worth of undead created

Or do the multipliers actually multiply?

i.e:
9(2*2)= 36 hd of undead.

Any help is appreciated!

[Segev]

In this case, the numbers actually multiply, because it's not a "doubling" as a bonus that is the first instance. 2xCL is just the formula, not a bonus to your undead-creating skills that doubles it.

[Asteron]

In this case, the numbers actually multiply, because it's not a "doubling" as a bonus that is the first instance. 2xCL is just the formula, not a bonus to your undead-creating skills that doubles it.

Gotcha. Thanks!