@inproceedings{trygve1954on,
title={On a special class of diophantine equations of the second degree},
author={Trygve Nagell},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203418190534903},
booktitle={Arkiv for Matematik},
volume={3},
number={1},
pages={51-65},
year={1954},
}