@article{MZM_1972_12_2_a5,
     author = {V. V. Ermakov},
     title = {A problem of {Ulam}},
     journal = {Matemati\v{c}eskie zametki},
     pages = {155--156},
     publisher = {mathdoc},
     volume = {12},
     number = {2},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1972_12_2_a5/}
}