
arXiv: 1412.3001
An m-endomorphism of a free semigroup is an endomorphism that sends every generator to a word of length at most m. Two m-endomorphisms are combinatorially equivalent if they are conjugate under an automorphism of the semigroup. In this paper, we specialize an argument of N. G. de Bruijn to produce a formula for the number of combinatorial equivalence classes of m-endomorphisms on a rank-n semigroup. From this formula, we derive several little-known integer sequences.
To appear in Involve: A Journal of Mathematics
Group Theory (math.GR), 05A99 (Primary), 20M15 (Secondary), enumeration, 20M15, semigroup, FOS: Mathematics, free semigroup endomorphisms, 05A99, Mathematics - Combinatorics, Combinatorics (math.CO), Mathematics - Group Theory
Group Theory (math.GR), 05A99 (Primary), 20M15 (Secondary), enumeration, 20M15, semigroup, FOS: Mathematics, free semigroup endomorphisms, 05A99, Mathematics - Combinatorics, Combinatorics (math.CO), Mathematics - Group Theory
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