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 A046908 Number of irreducible posets with n labeled points. 1
 1, 1, 1, 7, 97, 2251, 80821, 4305127, 332273257, 36630174931, 5711638291981, 1249898984911567, 381230073532620577, 161042140788424003291, 93667063572594041040421, 74610767840852891620692727, 80997478506602342803118178457, 119313601058907927882431190269731, 237541348427311374857037021264415741 (list; graph; refs; listen; history; text; internal format)
 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 G. Brinkmann,  B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147-179 (Table III, up to 18 points) 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

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Last modified May 7 19:47 EDT 2021. Contains 343652 sequences. (Running on oeis4.)