This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A279551 #26 Sep 02 2025 21:56:24 %S A279551 1,1,2,4,10,27,79,247,816,2822,10158,37875,145695,576288,2337412, %T A279551 9698820,41089107,177424188,779699793,3482575169,15791709187, %U A279551 72621800171,338388714955,1596314968112,7618218238583,36756086159343,179176803145900,882002961543492 %N A279551 Number of length n inversion sequences avoiding the patterns 000, 010, 110, and 120. %C A279551 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 and e_i >= e_k. This is the same as the set of length n inversion sequences avoiding 000, 010, 110, and 120. %H A279551 Nicholas R. Beaton, <a href="/A279551/b279551.txt">Table of n, a(n) for n = 0..65</a> %H A279551 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. %e A279551 For n=3, the inversion sequences are 001, 002, 011, 012. %e A279551 For n=4, the inversion sequences are 0011, 0012, 0013, 0021, 0022, 0023, 0112, 0113, 0122, 0123. %Y A279551 Cf. A263777, A263778, A263779, A263780, A279552, A279553, A279554, A279555, A279556, A279557, A279558, A279559, A279560, A279561, A279562, A279563, A279564, A279565, A279566, A279567, A279568, A279569, A279570, A279571, A279572, A279573. %K A279551 nonn,changed %O A279551 0,3 %A A279551 _Megan A. Martinez_, Dec 15 2016 %E A279551 Typo in comment corrected and a(10)-a(27) added by _Alois P. Heinz_, Feb 22 2017