@article{DAN_1971_196_4_a0,
     author = {A. N. Andrianov and O. M. Fomenko},
     title = {Distribution of the norms of the hyperbolic elements of the modular group and the class number of indefinite binary quadratic forms},
     journal = {Doklady Akademii Nauk},
     pages = {743--745},
     publisher = {mathdoc},
     volume = {196},
     number = {4},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_196_4_a0/}
}