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# ab!

I was wondering about ab! (a and b are integers, ! is factorial). Do we first multiply a and b then factorial the product or do we factorial the b and then multiply.

Note by Djordje Marjanovic
4 years, 8 months ago

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Depends on the problem statement. Usually either $$(\overline{ab})!, (ab)!, a\cdot b!$$ is given so you don't need to worry. If it is ambigious, ask the composer. But I would treat this as $$(ab)!$$.

- 4 years, 8 months ago

if you are referring to (a*b)! then you should multiply them first and then find the factorial.

- 4 years, 8 months ago

If the problem states explicitly that ab is a two digit number, you should find the factorial of the two digit number. Like $$a=2,b=1$$, calculate 21!.

- 4 years, 8 months ago

You are necessitated to multiply them first and then evaluate the factorial. Think of $$(2*3)!=720$$, and $$2*3!=12$$. See the difference?

- 4 years, 8 months ago