@article{10_4153_CMB_2011_118_9,
     author = {Mollin, R. A. and Srinivasan, A.},
     title = {Pell {Equations:} {Non-Principal} {Lagrange} {Criteria} and {Central} {Norms}},
     journal = {Canadian mathematical bulletin},
     pages = {774--782},
     year = {2012},
     volume = {55},
     number = {4},
     doi = {10.4153/CMB-2011-118-9},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2011-118-9/}
}