English

A New Quantity Counted by OEIS Sequence A006012

Combinatorics 2017-06-28 v2

Abstract

We prove an existing conjecture that the sequence defined recursively by a1=1,a2=2,an=4an12an2a_1=1, a_2=2, a_n=4a_{n-1}-2a_{n-2} counts the number of length-nn permutations avoiding the four generalized permutation patterns 1-32-4, 1-42-3, 2-31-4, and 2-41-3.

Keywords

Cite

@article{arxiv.1706.07064,
  title  = {A New Quantity Counted by OEIS Sequence A006012},
  author = {Yonah Biers-Ariel},
  journal= {arXiv preprint arXiv:1706.07064},
  year   = {2017}
}
R2 v1 2026-06-22T20:25:41.819Z