@article{JIS_2007__10_3_a6,
     author = {Kolli, Messaoud},
     title = {Direct and elementary approach to enumerate topologies on a finite set},
     journal = {Journal of integer sequences},
     publisher = {mathdoc},
     volume = {10},
     number = {3},
     year = {2007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2007__10_3_a6/}
}