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%I #28 Jul 15 2024 10:38:21
%S 1,1,2,6,23,103,515,2803,16334,100700,650905,4380595,30528410,
%T 219352058,1619260140,12245357074,94636062782,745907086918,
%U 5985448211508,48824435255942,404330087326924,3395418226577756,28884708430087203,248696210256230427
%N Number of inversion sequences avoiding pattern 120.
%C Number of length n inversion sequences avoiding e_k < e_i < e_j for i<j<k. A length n inversion sequence e_1,e_2,...,e_n consists of nonnegative integers e_t <= t-1. - _Alois P. Heinz_, Dec 20 2016
%H Jay Pantone, <a href="/A263778/b263778.txt">Table of n, a(n) for n = 0..200</a>
%H Sylvie Corteel, Megan A. Martinez, Carla D. Savage, and Michael Weselcouch, <a href="http://arxiv.org/abs/1510.05434">Patterns in Inversion Sequences I</a>, arXiv:1510.05434 [math.CO], 2015.
%H Toufik Mansour and Mark Shattuck, <a href="https://doi.org/10.1515/puma-2015-0016">Pattern Avoidance in Inversion Sequences</a>, Pure Math. Appl. (PU.M.A.) 25 (2015), no. 2, 157-176.
%H Megan A. Martinez and Carla D. Savage, <a href="https://arxiv.org/abs/1609.08106">Patterns in Inversion Sequences II: Inversion Sequences Avoiding Triples of Relations</a>, arXiv:1609.08106 [math.CO], 2016.
%H Jay Pantone, <a href="https://arxiv.org/abs/2310.19632">The enumeration of inversion sequences avoiding the patterns 201 and 210</a>, arXiv:2310.19632 [math.CO], 2023.
%H Benjamin Testart, <a href="https://arxiv.org/abs/2407.07701">Completing the enumeration of inversion sequences avoiding one or two patterns of length 3</a>, arXiv:2407.07701 [math.CO], 2024. See p. 2.
%Y Cf. A263777, A263779, A263780.
%K nonn
%O 0,3
%A _Michel Marcus_, Oct 26 2015
%E a(0)=1 prepended by _Alois P. Heinz_, Dec 15 2016
%E a(10)-a(23) from _Alois P. Heinz_, Dec 20 2016