Journal of Integer Sequences, Vol. 20 (2017), Article 17.8.3

The Number of Permutations Avoiding a Set of Generalized Permutation Patterns

Yonah Biers-Ariel
Department of Mathematics
Rutgers University
Piscataway, NJ 08854


We prove a conjecture that the sequence defined recursively by a1 = 1, a2 = 2, an = 4an-1 - 2an-2 counts the number of length-n permutations avoiding the four generalized permutation patterns 1-32-4, 1-42-3, 2-31-4, and 2-41-3.

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(Concerned with sequences A006012.)

Received July 29 2017; revised version received August 29 2017. Published in Journal of Integer Sequences, August 31 2017.

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