A combinatorial proof of the log-concavity of a famous sequence counting permutations.
A combinatorial proof of the sum of -cubes.
A combinatorial property and power graphs of semigroups
Research on combinatorial properties of sequences in groups and semigroups originates from Bernhard Neumann's theorem answering a question of Paul Erd"{o}s. For results on related combinatorial properties of sequences in semigroups we refer to the book [3]. In 2000 the authors introduced a new combinatorial property and described all groups satisfying it. The present paper extends this result to all semigroups.
A combinatorial ranking problem.
A combinatorial ranking problem. (Short Communication).
A combinatorial representation with Schröder paths of biorthogonality of Laurent biorthogonal polynomials.
A combinatorial theorem for a symmetric triangulation of the sphere
A common generalization of binomial coefficients, Stirling numbers and Gaussian coefficients.
A common generalization of binomial coefficients, Stirling numbers and Gaussian Coefficientes
A common generalization of some identities.
A common generating function for Catalan numbers and other integer sequences.
A common recursion for Laplacians of matroids and shifted simplicial complexes.
A comparison of two upper bounds on the permanent of -matrices. (Ein Vergleich zweier oberer Schranken für die Permanente von -Matrizen.)
A complete annotated bibliography of work related to Sidon sequences.
A complete categorization of when generalized Tribonacci sequences can be avoided by additive partitions.
A complete grammar for decomposing a family of graphs into 3-connected components.
A concise proof of the Littlewood-Richardson rule.
A Conjecture Concerning The Existence Of Certain Combinatorial Designs.
A conjecture of Biggs concerning the resistance of a distance-regular graph.
A conjecture of Stanley on alternating permutations.