A046908 Number of irreducible posets with n labeled points.

1, 1, 1, 7, 97, 2251, 80821, 4305127, 332273257, 36630174931, 5711638291981, 1249898984911567, 381230073532620577, 161042140788424003291, 93667063572594041040421, 74610767840852891620692727, 80997478506602342803118178457, 119313601058907927882431190269731, 237541348427311374857037021264415741

Offset

0,4

References

J. A. Wright, There are 718 6-point topologies, quasi-orderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70T-A106.

Links

Table of n, a(n) for n=0..18.

G. Brinkmann,  B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147-179 (Table III, up to 18 points)

J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences

Index entries for sequences related to posets

Formula

E.g.f.: A(x) = 2-1/B(x), where B(x) is e.g.f. of A001035. - Vladeta Jovovic, Jan 10 2006

Mathematica

A001035 = Cases[Import["https://oeis.org/A001035/b001035.txt", "Table"], {_, _}][[All, 2]]; lg = Length[A001035];
B[x_] = Sum[A001035[[n + 1]] x^n/n!, {n, 0, lg - 1}];
A[x_] = 2 - 1/B[x];
CoefficientList[A[x] + O[x]^lg, x]*Range[0, lg - 1]! (* Jean-François Alcover, Jan 01 2020 *)

Crossrefs

Cf. A046907.

Sequence in context: A003710 A027837 A174315 * A005014 A201063 A333246

Adjacent sequences: A046905 A046906 A046907 * A046909 A046910 A046911

Keyword

nonn

Author

John A. Wright.

Extensions

More terms from Vladeta Jovovic, Jan 10 2006

a(16)-a(18) from A001035 by Jean-François Alcover, Jan 01 2020

Status

approved