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 A221494 #15 Aug 01 2025 03:26:14 %S A221494 1,1,1,3,5,1,12,28,16,2,55,165,152,47,4,273,1001,1265,658,136,9,1428, %T A221494 6188,9919,7315,2547,392,21,7752,38760,75208,71981,35975,9252,1130,51, %U A221494 43263,245157,558144,657356,431599,159701,32286,3262,127,246675,1562275 %N A221494 Table read by downward diagonals: T(n,k) = number of skeleta of (3+1)-free posets with n clone sets and k tangles. %H A221494 M. Guay-Paquet, A. H. Morales, and E. Rowland, <a href="http://arxiv.org/abs/1212.5356">Structure and enumeration of (3+1)-free posets (extended abstract)</a>, arXiv:1212.5356 [math.CO], 2012. %F A221494 G.f.: S(x, y) is the unique power series solution of the equation S(x, y) = 1 + S(x, y)^2 * x / (1 + x) + S(x, y)^3 * y. %e A221494 There are 28 skeleta of (3+1)-free posets with 1 clone set and 2 tangles. %e A221494 Table begins %e A221494 1 1 3 12 55 273 ... %e A221494 1 5 28 165 1001 6188 ... %e A221494 1 16 152 1265 9919 75208 ... %e A221494 2 47 658 7315 71981 657356 ... %e A221494 4 136 2547 35975 431599 4660516 ... %e A221494 9 392 9252 159701 2277821 28589750 ... %e A221494 ...................................... %Y A221494 Cf. A079145, A079146, A221492, A221493 %K A221494 nonn,easy,tabl %O A221494 0,4 %A A221494 _Mathieu Guay-Paquet_, Jan 18 2013