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@article{MZM_1991_49_5_a20, author = {S. A. Zakharov}, title = {The number of solutions of the equation $ax_1x_2+bx_3x_4=N$}, journal = {Matemati\v{c}eskie zametki}, pages = {151--152}, publisher = {mathdoc}, volume = {49}, number = {5}, year = {1991}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1991_49_5_a20/} }
S. A. Zakharov. The number of solutions of the equation $ax_1x_2+bx_3x_4=N$. Matematičeskie zametki, Tome 49 (1991) no. 5, pp. 151-152. http://geodesic.mathdoc.fr/item/MZM_1991_49_5_a20/