Monotonic growth-constant conjecture for 132-avoiding permutations with bounded adjacency

From papers

Let An(m)A_n^{(m)} be the class of permutations in SnS_n that avoid 132132 and satisfy πi+1πim|\pi_{i+1}-\pi_i|\leq m, with mm fixed. Define the exponential growth constant, when the limit exists, by

αm=limn(An(m))1/n.\alpha_m = \lim_{n\to\infty} (A_n^{(m)})^{1/n}.

Monotonic growth-constant conjecture. For fixed mm, the limit αm\alpha_m exists, and

1=α1<α2<α3<<4.1=\alpha_1<\alpha_2<\alpha_3<\cdots<4.

Moreover,

limmαm=4.\lim_{m\to\infty}\alpha_m=4.

The known cases include growth rate 11 for m=1m=1, growth constant approximately 1.465571.46557 for m=2m=2, and the Catalan growth rate 44 when the adjacency bound is at least n1n-1. The strict monotonicity and limiting assertion remain conjectural in the source.

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Sources & referencesView supporting material

Primary source

Nathaniel Nadler, “On 132-Avoiding Permutations with an Adjacency Constraint”, arXiv:2604.22135 (2026).

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