@article{10_1017_S0017089500002305,
     author = {Beineke, L. W. and Pippert, R. E.},
     title = {On the enumeration of planar trees of hexagons},
     journal = {Glasgow mathematical journal},
     pages = {131--147},
     year = {1974},
     volume = {15},
     number = {2},
     doi = {10.1017/S0017089500002305},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500002305/}
}