Riordan group involutions and the∆-sequence
نویسندگان
چکیده
Several important combinatorial arrays, after inserting some minus signs, turn out to be involutions when considered as lower triangular matrices. Among these are the Pascal, RNA, and directed animal matrices. These examples and many others are in the Bell subgroup of the Riordan group. We characterize all such pseudo-involutions by means of a single sequence called the ∆-sequence. Finally we compute the ∆-sequences for the powers of a pseudo-involution in the Bell subgroup. © 2009 Elsevier B.V. All rights reserved.
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