Counting Subwords in Non-Decreasing Dyck Paths
Rigoberto Flórez
Department of Mathematical Sciences
The Citadel
Charleston, SC 29409
USA
Leandro Junes
Department of Mathematics
PennWest California
California, PA 15419
USA
Luisa M. Montoya and José L. Ramírez
Departamento de Matemáticas
Universidad Nacional de Colombia
Bogotá
Colombia
Abstract:
A Dyck path is non-decreasing if the y-coordinates of its valleys, which
are local minima along the path, form a non-decreasing sequence. To
count the number of subpaths (or subwords) within non-decreasing Dyck
paths, we use generating functions and recursive relations. These
techniques enable us to count subpaths of various lengths, such as
two, three, four, and five, while considering both the length and the
number of subwords. Using constructive recursive proofs, we establish
a combinatorial interpretation of the counting process, expressing
the results as linear combinations of Fibonacci and Lucas numbers. In
several cases, we provide new interpretations of sequences from the
On-Line Encyclopedia of Integer Sequences (OEIS).
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(Concerned with sequences
A000108
A001870
A001871
A002212
A030267
A033321
A038731
A039598
A054444
A059502
A105306
A105693
A121463
A121466
A122737
A153342
A197649
A238846
A304429
A375995
A377670
A377679
A377857
A377866
A377867
A378383.)
Received November 5 2024; revised version received February 12 2025.
Published in Journal of Integer Sequences,
February 13 2025.
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