@article{MAN_1957__133_160561,
     author = {B. Hornfeck and E. Wirsing},
     title = {\"Uber die {H\"aufigkeit} vollkommener {Zahlen.}},
     journal = {Mathematische Annalen},
     pages = {431--438},
     publisher = {mathdoc},
     volume = {133},
     year = {1957},
     zbl = {0084.04204},
     url = {http://geodesic.mathdoc.fr/item/MAN_1957__133_160561/}
}