@article{JIS_2017__20_6_a3,
     author = {Janji\'c, Milan},
     title = {Some formulas for numbers of restricted words},
     journal = {Journal of integer sequences},
     publisher = {mathdoc},
     volume = {20},
     number = {6},
     year = {2017},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2017__20_6_a3/}
}