Here's the pmf:

$\displaystyle p_{X,Y}(i, j) = \frac{2}{n(n+1)} \mbox{ for } 1\leq j\leq i\leq n, n > 0$

I got the first part, which is verifying that this is a legitimate joint pmf, however I am stuck on finding the marginal pmf. I know that marginal pmf of X would be:

$\displaystyle p_{X}(i) = \sum_j p_{X,Y}(i, j)$

But wouldn't that just be $\displaystyle (n)(\frac{2}{n(n+1)}$ in this case? But somehow I don't think it's that easy.