A046907 Number of isomorphism classes of irreducible posets with n labeled points.

1, 1, 1, 2, 7, 31, 184, 1351, 12524, 146468, 2177570, 41374407, 1008220289, 31559446774, 1269310589336, 65562045668340, 4345161435996517

Offset: 0

Author

John A. Wright

Keywords

• nonn
• more

Links

• G. Brinkmann, B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147-179 (Table 1).
• J. A. Wright, There are 718 6-point topologies, quasi-orderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70T-A106.
• J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences
• Index entries for sequences related to posets

Crossrefs

Cf. A046908.

Programs

Mathematica

A000112 = Cases[Import["https://oeis.org/A000112/b000112.txt", "Table"], {, }][[All, 2]];
B[x_] = A000112.x^Range[0, Length[A000112] - 1];
A[x_] = 2 - 1/B[x];
CoefficientList[A[x] + O[x]^Length[A000112], x] (* Jean-François Alcover, Jan 01 2020 *)

Formula

G.f.: A(x) = 2-1/B(x), where B(x) is g.f. of A000112. - Vladeta Jovovic, Jan 15 2006

Extensions

More terms from Vladeta Jovovic, Jan 15 2006