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 010, 110, and 120.
LINKS
Megan A. Martinez, Carla D. Savage, Patterns in Inversion Sequences II: Inversion Sequences Avoiding Triples of Relations, arXiv:1609.08106 [math.CO], 2016-2018.
EXAMPLE
The length 3 inversion sequences avoiding (010, 110, 120) are 000, 001, 002, 011, 012
The length 4 inversion sequences avoiding (010, 110, 120) are 0000, 0001, 0002, 0003, 0011, 0012, 0013, 0021, 0022, 0023, 0111, 0112, 0113, 0122, 0123.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Megan A. Martinez, Dec 16 2016
EXTENSIONS
a(10)-a(11) from Alois P. Heinz, Feb 24 2017
a(12)-a(16) from Bert Dobbelaere, Dec 30 2018
STATUS
approved