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A279573 Number of length n inversion sequences avoiding the patterns 120 and 210. 23
1, 1, 2, 6, 23, 102, 499, 2625, 14601, 84847, 510614, 3161964, 20050770, 129718404, 853689031, 5701759424, 38574689104, 263936457042, 1824032887177, 12718193293888, 89386742081688, 632746535420834, 4508140253686638, 32308561883462867, 232790342330880572 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
A length n inversion sequence e_1e_2...e_n is a sequence of integers where 0 <= e_i <= i-1. The term a(n) counts those length n inversion sequences with no entries e_i, e_j, e_k (where i<j<k) such that e_i <> e_j > e_k and e_i > e_k. This is the same as the set of length n inversion sequences avoiding 120 and 210.
LINKS
Megan A. Martinez, Carla D. Savage, Patterns in Inversion Sequences II: Inversion Sequences Avoiding Triples of Relations, arXiv:1609.08106 [math.CO], 2016.
Chunyan Yan, Zhicong Lin, Inversion sequences avoiding pairs of patterns, arXiv:1912.03674 [math.CO], 2019.
FORMULA
a(n) ~ c * 8^n / n^(3/2), where c = 0.0013548789253263217919... - Vaclav Kotesovec, Oct 07 2021
EXAMPLE
The length 4 inversion sequences avoiding (120,210) are 0000, 0001, 0002, 0003, 0010, 0011, 0012, 0013, 0020, 0021, 0022, 0023, 0100, 0101, 0102, 0103, 0110, 0111, 0112, 0113, 0121, 0122, 0123.
CROSSREFS
Sequence in context: A245389 A088929 A356111 * A174193 A238639 A226995
KEYWORD
nonn
AUTHOR
Megan A. Martinez, Feb 21 2017
EXTENSIONS
a(10)-a(24) from Alois P. Heinz, Feb 21 2017
STATUS
approved

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Last modified March 28 07:48 EDT 2024. Contains 371235 sequences. (Running on oeis4.)