@incollection{AST_1987__147-148__259_0,
     author = {Arenas, Angela},
     title = {On positive integers representable as a sum of three squares},
     booktitle = {Journ\'ees arithm\'etiques de Besan\c{c}on},
     series = {Ast\'erisque},
     pages = {259--263},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {147-148},
     year = {1987},
     zbl = {0623.10034},
     language = {en},
     url = {http://archive.numdam.org/item/AST_1987__147-148__259_0/}
}