Write the equation as Suppose And so So we have c =1.The equation becomes (1+a)(1+b) = 2ab or 1+a+b = ab.Since a divides ab and a, we have a divides (b+1) and similarly b divides a+1.This yields Also a divides b+1 means a is not equal to b (as b does not divide b+1). So a = b+1.So the equation (a+1)(b+1) = 2ab now becomes a(a+1) = 2a (a-1) so a=3, and b=2.So (a,b,c) = (3,2,1) is the only solution. This solution satisfies the relation a+b+c=abc