  Graham and Sloane proposed in 1980 a conjecture stating that every tree has a
harmonious labelling, a graph labelling closely related to additive base. Very
limited results on this conjecture are known. In this paper, we proposed a
computational approach to this conjecture by checking trees with limited size.
With a hybrid algorithm, we are able to show that every tree with at most 31
nodes is harmonious, extending the best previous result in this direction.
