@article{JRAM_1973__260_151311,
     author = {F.T. Howard},
     title = {Properties of the van der {Pol} numbers and polynomials.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {35--46},
     publisher = {mathdoc},
     volume = {260},
     year = {1973},
     zbl = {0254.10013},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1973__260_151311/}
}