If \( f(x) = \frac{x(x-1)}{2} \), then what is the expression for \( f(x+2) \)? The original answer is in the form \(\frac{(x+k)f(x+m)}{n*x}\). Please find the value of k + m + n.

Let's think step by step and output the final answer within \boxed{}.
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