There are 50,024 Kirkman triple systems of order 21 admitting an automorphism of order 2. There are 13,280 Kirkman triple systems of order 21 admitting an automorphism of order 3. Together with the 192 known systems and some simple exchange operations, this leads to a collection of 63,745 nonisomorphic Kirkman triple systems of order 21. This includes all KTS(21)s having a nontrivial automorphism group. None of these is doubly resolvable. Four are quadrilateral-free, providing the first examples of such a KTS(21).
机构:
Hebei Normal Univ, Coll Occupat Technol, Shijiazhuang 050031, Peoples R ChinaHebei Normal Univ, Coll Occupat Technol, Shijiazhuang 050031, Peoples R China
Yuan, Landang
Kang, Qingde
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Hebei Normal Univ, Inst Math, Shijiazhuang 050016, Peoples R ChinaHebei Normal Univ, Coll Occupat Technol, Shijiazhuang 050031, Peoples R China