Geodesic
A recurrent algorithm for solving a combinatorial problem on arrangements with restrictions
Diskretnaya Matematika, Tome 11 (1999) no. 2, pp. 112-117 
I. I. Trub. A recurrent algorithm for solving a combinatorial problem on arrangements with restrictions. Diskretnaya Matematika, Tome 11 (1999) no. 2, pp. 112-117. http://geodesic.mathdoc.fr/item/DM_1999_11_2_a6/
@article{DM_1999_11_2_a6,
     author = {I. I. Trub},
     title = {A recurrent algorithm for solving a combinatorial problem on arrangements with restrictions},
     journal = {Diskretnaya Matematika},
     pages = {112--117},
     year = {1999},
     volume = {11},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_1999_11_2_a6/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

We consider $N$ groups of elements such that the elements in different groups are distinct and each group consists of $Q$ identical elements. How many ways are there to arrange these $QN$ elements so that the permutation obtained contains exactly $L$ pairs of adjacent identical elements, $0\leq L\leq N(Q-1)$? The particular case $L=0$ corresponds to calculating the number of permutations with no two adjacent identical elements.We suggest a recurrent algorithm for solving the problem and its generalization to the case where the groups may contain different numbers of elements.