@article{10_4064_fm_114_2_109_112,
     author = {J. Dudek},
     title = {Medial groupoids and {Mersenne} numbers},
     journal = {Fundamenta Mathematicae},
     pages = {109--112},
     publisher = {mathdoc},
     volume = {114},
     number = {2},
     year = {1981},
     doi = {10.4064/fm-114-2-109-112},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-114-2-109-112/}
}