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COMBINATORICS
2007
13 years 11 months ago
2007
Let Sn denote the symmetric group on [n] = {1, . . . , n}. A family I ⊆ Sn is intersecting if any two elements of I have at least one common entry. It is known that the only int...
COMBINATORICS
2007
13 years 11 months ago
2007
By introducing the notion of relative derangements of type B, also called signed relative derangements, which are defined in terms of signed permutations, we obtain a type B anal...
COMBINATORICS
2007
13 years 11 months ago
2007
We define an excedance number for the multi-colored permutation group i.e. the wreath product (Zr1 × · · · × Zrk ) Sn and calculate its multi-distribution with some natural ...
COMBINATORICS
2007
13 years 11 months ago
2007
Using a recent result of Chudnovsky, Seymour, and Sullivan, we slightly improve two bounds related to the Caccetta-Haggkvist Conjecture. Namely, we show that if α ≥ 0.35312, th...
COMBINATORICS
2007
13 years 11 months ago
2007
We determine the exact and asymptotic number of unlabeled outerplanar graphs. The exact number gn of unlabeled outerplanar graphs on n vertices can be computed in polynomial time,...