simplifying sums



I am having trouble with finite sums. I started looking at some simple 
examples to try to get a better grasp--please let me know if there's a 
better way to handle sum() calculations. While 'sum(1,i,1,n)' returns 
'n' as it should, sum(i,i,1,n) remains in open form. From describe(sum) 
I picked up that I need to do sum(i,i,1,n),simpsum to get the expected

                                      2
                                     n  + n
(%o9)                               ------
                                       2


My first newbie question is what is that construct 'sum(),simpsum'? is 
simpsum a procedure evaluated on output of sum(), or some global flag?
The help doesn't describe it, but just mention it in the examples.

My real summation formula is sum(binomial(k+1,2)^(n-k),k,1,n) (it has to 
do with a number of ways you can configure an electronic circiut with n 
components). I wasn't able to simplify this expression in any way; 
please let me know if you have any suggestions.