@article{JIS_2015__18_8_a4,
     author = {Lam, Peter Cho-Ho},
     title = {Representation of integers using $a^2 + b^2 - dc^2$},
     journal = {Journal of integer sequences},
     publisher = {mathdoc},
     volume = {18},
     number = {8},
     year = {2015},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2015__18_8_a4/}
}