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2. On the limit points of a function connected with the three-square problem;Chakrabarti, M. C.;Bull. Calcutta Math. Soc.,1940
3. R. Descartes, Oeuvres, vol. 2, Paris, Cerf, 1898.
4. L. E. Dickson, History of the theory of numbers, New York, Chelsea Publishing Company, 1952.
5. E. Dubouis, L’Interm. des Math. vol. 18 (1911) pp. 55-56, 224-225.