@article{JIS_2006__9_2_a6,
     author = {Benoumhani,  Moussa},
     title = {The number of topologies on a finite set},
     journal = {Journal of integer sequences},
     year = {2006},
     volume = {9},
     number = {2},
     zbl = {1103.11007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2006__9_2_a6/}
}