diophantine equation 1/x + 1/y = 1/n

hello everybody i want to know how many distinct solution of
equation(1/x+1/y=1/n) for given value of n . for example if n=4 then
three distinct solution (5,20)(6,12) and (8,8).
plz tell me the algorithm to solve this problem . thnkx in advance .

.