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A046912 Number of irreducible quasiorders with n labeled points. 1
1, 1, 2, 11, 147, 3412, 121553, 6353629, 476850636, 50811255045, 7636459252135, 1610584897516674, 474333338553730879, 194055026319667963777, 109692570582311591696890, 85221064877720762475072503, 90542406571528792666541430863, 130936936785995060562730057163556, 256634185641525450158992588551158389 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

FORMULA

E.g.f.: A(x) = 2-1/B(x), where B(x) is e.g.f. of A000798. - Vladeta Jovovic, Jan 10 2006

MATHEMATICA

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 *)

CROSSREFS

Cf. A046911.

Sequence in context: A268743 A204243 A203203 * A185245 A006122 A111014

Adjacent sequences:  A046909 A046910 A046911 * A046913 A046914 A046915

KEYWORD

nonn,more

AUTHOR

John A. Wright.

EXTENSIONS

Corrected and extended by Vladeta Jovovic, Jan 10 2006

a(16)-a(18) from A000798 by Jean-François Alcover, Jan 01 2020

STATUS

approved

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Last modified April 17 09:29 EDT 2021. Contains 343064 sequences. (Running on oeis4.)