@article{JIS_2003__6_3_a2,
     author = {Ufnarovski,  Victor and \r{A}hlander,  Bo},
     title = {How to differentiate a number},
     journal = {Journal of integer sequences},
     year = {2003},
     volume = {6},
     number = {3},
     zbl = {1142.11305},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2003__6_3_a2/}
}