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A046912
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Number of irreducible quasiorders with n labeled points.
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1
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1, 1, 2, 11, 147, 3412, 121553, 6353629, 476850636, 50811255045, 7636459252135, 1610584897516674, 474333338553730879, 194055026319667963777, 109692570582311591696890, 85221064877720762475072503, 90542406571528792666541430863, 130936936785995060562730057163556, 256634185641525450158992588551158389
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..18.
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
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FORMULA
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E.g.f.: A(x) = 2-1/B(x), where B(x) is e.g.f. of A000798. - Vladeta Jovovic, Jan 10 2006
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MATHEMATICA
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A000798 = Cases[Import["https://oeis.org/A000798/b000798.txt", "Table"], {_, _}][[All, 2]]; lg = Length[A000798];
B[x_] = Sum[A000798[[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 *)
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CROSSREFS
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Cf. A046911.
Sequence in context: A268743 A204243 A203203 * A185245 A006122 A111014
Adjacent sequences: A046909 A046910 A046911 * A046913 A046914 A046915
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KEYWORD
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nonn,more
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AUTHOR
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John A. Wright.
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EXTENSIONS
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Corrected and extended by Vladeta Jovovic, Jan 10 2006
a(16)-a(18) from A000798 by Jean-François Alcover, Jan 01 2020
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STATUS
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approved
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