@article{MAN_1980__252_163456,
     author = {Jing Yu},
     title = {A {Cuspidal} {Class} {Number} {Formula} for the {Modular} {Curves} {X1(N).}},
     journal = {Mathematische Annalen},
     pages = {197--216},
     publisher = {mathdoc},
     volume = {252},
     year = {1980},
     zbl = {0426.12003},
     url = {http://geodesic.mathdoc.fr/item/MAN_1980__252_163456/}
}