This is a good start as you are trying, as a first step, to operate a bit how you would proceed by hand, element by element in a loop.
The next step is to realize that MATLAB can operate on arrays:
>> x = 1 : 3 : 11
x =
1 4 7 10
defines a row vector, it is actually how you define the pool of values that your loop variable must take through iterations. Now say you have a vector of values, would you be able to compute their product without using a loop? You probably saw the function SUM, maybe there is an equivalent for products? [-> Google or Doc]
Here is an element-wise square and a sum to illustrate usual operations with arrays:
>> x.^2 % Element-wise square.
ans =
1 16 49 100
>> sum( x ) % Sum of all elements.
ans =
22
Once you understand this you'll know two things: how to build vectors of linearly spaced elements from a lower bound to an upper bound, and how to compute their product.
You will be in a situation where you know how to define the upper bound as it is the input of the function, but you will have to find a way to define the lower bound, which is a number that is either 1 or 2 depending the parity of the input. Maybe there is a way .. maybe you almost found it already (!)
