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 A375923 #10 Sep 12 2024 07:48:59 %S A375923 1,1,2,6,24,112,582,3272,19550,122628,800392,5400342,37475474, %T A375923 266412680,1934033968,14300538652,107471798112,819442325086, %U A375923 6329551390064,49465665347580,390692732060804,3115700976866356,25067250869113332,203317147838575616,1661425311693158000 %N A375923 Number of permutations of size n which are both two-clumped and co-two-clumped. %C A375923 Two-clumped permutations are (3-51-2-4, 3-51-4-2, 2-4-51-3, 4-2-51-3)-avoiding permutations. Co-two-clumped permutations are (3-15-2-4, 3-15-4-2, 2-4-15-3, 4-2-15-3)-avoiding permutations. Thus, this sequence enumerates permutations that avoid all these eight patterns. %C A375923 a(n) is also the number of strong (=generic) rectangulations of size n whose strong poset is totally ordered. %H A375923 Andrei Asinowski, Jean Cardinal, Stefan Felsner, and Éric Fusy, <a href="https://arxiv.org/abs/2402.01483">Combinatorics of rectangulations: Old and new bijections</a>, arXiv:2402.01483 [math.CO], 2024, page 29. %Y A375923 Cf. A342141 (number of two-clumped permutations). %Y A375923 Cf. A001181 (Baxter numbers: number of (twisted-)Baxter permutations). %Y A375923 Cf. A348351 (number of permutations which are both twisted-Baxter and co-twisted-Baxter). %K A375923 nonn %O A375923 0,3 %A A375923 _Andrei Asinowski_, Sep 02 2024