A221493 -id:A221493 - cp's OEIS frontend

A079145 Number of labeled semitransitive orders on n elements: (1+3)-free posets.

1, 3, 19, 195, 2791, 51423, 1167979, 32067675, 1064281951, 43806954183, 2376985075939, 186194963282595, 22598045194449271, 4259417828951807343, 1200382884654622348699, 490727012583769876310955, 286998078380075662131967951, 238889878466868543045084230103

Offset: 1

Detlef Pauly (dettodet(AT)yahoo.de), Dec 27 2002

M. Guay-Paquet, A. H. Morales, E. Rowland, Structure and enumeration of (3+1)-free posets (extended abstract), arXiv:1212.5356 [math.CO], 2012.

Cf. A079146 (unlabeled semitransitive orders).

E.g.f.: S(e^x-1, T(x)), where S(x, y) is the g.f. for A221494 and T(x) is the e.g.f. for A221493. [Mathieu Guay-Paquet, Jan 18 2013]

More terms from Mathieu Guay-Paquet, Jan 18 2013

A221492 Number of tangled bicolored graphs on n unlabeled vertices.

Original entry on oeis.org

0, 0, 0, 0, 1, 2, 10, 34, 158, 804, 4876, 35516, 319719, 3636064, 53349918, 1025758444, 26132964903, 888605372756, 40526634099476, 2487361532245964, 205991405080129554, 23065538883807036798, 3498567662956243132910

Offset: 0

Mathieu Guay-Paquet, Jan 18 2013

nonn

A bicolored graph on n labeled vertices, k of which are black, and (n-k) of which are white, can be represented as a k X (n-k) matrix, where the (i,j) entry is 1 if the i-th black vertex is adjacent to the j-th white vertex, and 0 otherwise. Then, the graph is tangled if (1) the matrix does not have any rows or columns of all 0's or all 1's; and (2) it is not possible to permute the rows of the matrix and the columns of the matrix to obtain a matrix of the form
[ A | J ]
[---+---]
[ 0 | B ]
where the top right block J consists of all 1's, and the bottom left block 0 consists of all 0's.

			The only tangled bicolored graph on 4 vertices (up to isomorphism) consists of 2 black vertices, 2 white vertices, and 2 edges, with each black vertex joined to a different white vertex.

M. Guay-Paquet, A. H. Morales, E. Rowland, Structure and enumeration of (3+1)-free posets (extended abstract), arXiv:1212.5356 [math.CO], 2012.

Cf. A221493, A079146.

terms = 23;
b[n_, i_] := b[n, i] = If[n == 0, {0}, If[i < 1, {}, Flatten @ Table[Map[ Function[{p}, p + j*x^i], b[n - i*j, i - 1]], {j, 0, n/i}]]];
g[n_, k_] := g[n, k] = Sum[Sum[2^Sum[Sum[GCD[i, j]*Coefficient[s, x, i]* Coefficient[t, x, j], {j, 1, Exponent[t, x]}], {i, 1, Exponent[s, x]}]/ Product[i^Coefficient[s, x, i]*Coefficient[s, x, i]!, {i, 1, Exponent[s, x]}]/Product[i^Coefficient[t, x, i]*Coefficient[t, x, i]!, {i, 1, Exponent[t, x]}], {t, b[n + k, n + k]}], {s, b[n, n]}];
A[n_, k_] := g[Min[n, k], Abs[n - k]];
A[d_] := Sum[A[n, d - n], {n, 0, d}];
B[x_] = Sum[A[d] x^d, {d, 0, terms}];
T[x_] = 1 - 2x - 1/B[x];
CoefficientList[T[x] + O[x]^terms, x] (* Jean-François Alcover, Jan 30 2019, after Alois P. Heinz in A049312 *)

G.f.: T(x) = 1 - 2*x - 1/(1+B(x)), where B(x) is the g.f. for A049312.

A221494 Table read by downward diagonals: T(n,k) = number of skeleta of (3+1)-free posets with n clone sets and k tangles.

Original entry on oeis.org

1, 1, 1, 3, 5, 1, 12, 28, 16, 2, 55, 165, 152, 47, 4, 273, 1001, 1265, 658, 136, 9, 1428, 6188, 9919, 7315, 2547, 392, 21, 7752, 38760, 75208, 71981, 35975, 9252, 1130, 51, 43263, 245157, 558144, 657356, 431599, 159701, 32286, 3262, 127, 246675, 1562275

Offset: 0

Mathieu Guay-Paquet, Jan 18 2013

			There are 28 skeleta of (3+1)-free posets with 1 clone set and 2 tangles.
Table begins
  1   1    3     12      55      273 ...
  1   5   28    165    1001     6188 ...
  1  16  152   1265    9919    75208 ...
  2  47  658   7315   71981   657356 ...
  4 136 2547  35975  431599  4660516 ...
  9 392 9252 159701 2277821 28589750 ...
  ......................................

M. Guay-Paquet, A. H. Morales, and E. Rowland, Structure and enumeration of (3+1)-free posets (extended abstract), arXiv:1212.5356 [math.CO], 2012.

Cf. A079145, A079146, A221492, A221493

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.

cp's OEIS Frontend

A079145 Number of labeled semitransitive orders on n elements: (1+3)-free posets.

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A221492 Number of tangled bicolored graphs on n unlabeled vertices.

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A221494 Table read by downward diagonals: T(n,k) = number of skeleta of (3+1)-free posets with n clone sets and k tangles.

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