@article{ZNSL_1979_91_a9,
     author = {L. A. Takhtadzhyan},
     title = {Asymptotic formula for the sum of the lengths of the periods of the quadratic irrationalities of discriminant~$D$},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {134--144},
     publisher = {mathdoc},
     volume = {91},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1979_91_a9/}
}