@inproceedings{frank1959the,
title={The number of homeomorphically irreducible trees, and other species},
author={Frank Harary, and Geert Prins},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203151524037880},
booktitle={Acta Mathematica},
volume={101},
number={1},
pages={141-162},
year={1959},
}
Frank Harary, and Geert Prins. The number of homeomorphically irreducible trees, and other species. 1959. Vol. 101. In Acta Mathematica. pp.141-162. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203151524037880.