Bulletin of the London Mathematical Society Advance Access published online on September 22, 2009
Bulletin of the London Mathematical Society, doi:10.1112/blms/bdp071
© 2009 London Mathematical Society
Smooth partitions and Chebyshev polynomials
Department of Mathematics
University of Haifa
31905 Haifa
Israel
Received 13 September 2008. Revision received 22 May 2009.
A partition of the set [n] = {1, 2, ..., n} is a collection {B1, ..., Bk} of nonempty disjoint subsets of [n] (called blocks) whose union equals [n]. A partition of [n] is said to be smooth if i
Bs implies that i + 1
Bs–1
Bs
Bs + 1 for all i
[n–1] (B0 = Bk + 1 =
). This paper presents the generating function for the number of k-block, smooth partitions of [n], written in terms of Chebyshev polynomials of the second kind. There follows a formula for the number of k-block, smooth partitions of [n] written in terms of trigonometric sums. Also, by first establishing a bijection between the set of smooth partitions of [n] and a class of symmetric Dyck paths of semilength 2n–1, we prove that the counting sequence for smooth partitions of [n] is Sloane's A005773.
2000 Mathematics Subject Classification 68R05, 05A05, 05A15, 05A16.