
A \(k\)-extended Langford sequence of defect \(d\) and length \(m\) is a sequence \(s_1,\dots,s_{2m+1}\) in which \(s_k=\varepsilon\), where \(\varepsilon\) is the null symbol and each other member of the sequence comes from the set \(S=\{d,d+1,\dots,d+m-1\}\). Each \(j\in S\) occurs exactly twice in the sequence and the two occurences are separated by exactly \(j-1\) symbols. In this paper necessary conditions for the existence of such a sequence are given and it is shown that when \(d=2,3\) these conditions are sufficient, too.
Permutations, words, matrices, Computational Theory and Mathematics, Special sequences and polynomials, extended Langford sequence, Discrete Mathematics and Combinatorics, Skolem sequence, Theoretical Computer Science
Permutations, words, matrices, Computational Theory and Mathematics, Special sequences and polynomials, extended Langford sequence, Discrete Mathematics and Combinatorics, Skolem sequence, Theoretical Computer Science
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