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 A189507 #21 May 20 2023 07:47:53 %S A189507 1,1,1,4,3,1,20,21,6,1,148,160,65,10,1,1348,1620,701,155,15,1,15104, %T A189507 19068,9324,2247,315,21,1,198144,264420,138016,38029,5908,574,28,1, %U A189507 2998656,4166880,2325740,692088,124029,13524,966,36,1,51290496,74011488,43448940,13945700,2723469,344961,27930,1530,45,1,979732224,1459381440,897020784,305142068,64711856,8996295,850905,53262,2310,55,1 %N A189507 Triangle read by rows: T(n,k) (n >= 0, 1 <= k <= n+1) are the signed Hultman numbers. %C A189507 "Signed" refers to the fact that these numbers are associated with signed permutations. The numbers themselves are positive. %H A189507 N. Alexeev, A. Pologova, M. A. Alekseyev, Generalized Hultman Numbers and Cycle Structures of Breakpoint Graphs, Journal of Computational Biology 24:2 (2017), 93-105. doi:<a href="http://doi.org/10.1089/cmb.2016.0190">10.1089/cmb.2016.0190</a> arXiv:<a href="http://arxiv.org/abs/1503.05285">1503.05285</a> %H A189507 Simona Grusea and Anthony Labarre, <a href="http://arxiv.org/abs/1104.3353">The distribution of cycles in breakpoint graphs of signed permutations</a>, arXiv:1104.3353v1 %e A189507 Triangle begins: %e A189507 1 %e A189507 1 1 %e A189507 4 3 1 %e A189507 20 21 6 1 %e A189507 148 160 65 10 1 %e A189507 1348 1620 701 155 15 1 %e A189507 15104 19068 9324 2247 315 21 1 %e A189507 ... %Y A189507 The first three columns give A001171, A189508, A189509. Cf. A164652. %K A189507 nonn,tabl %O A189507 0,4 %A A189507 _N. J. A. Sloane_, Apr 23 2011