@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/}
}