@article{10_4064_aa_7_4_399_407,
     author = {R. Rankin},
     title = {On the representation of a number as the sum of any number of squares, and in particular of twenty},
     journal = {Acta Arithmetica},
     pages = {399--407},
     publisher = {mathdoc},
     volume = {7},
     number = {4},
     year = {1961},
     doi = {10.4064/aa-7-4-399-407},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-7-4-399-407/}
}