

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
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OFFSET

0,4


REFERENCES

J. A. Wright, There are 718 6point topologies, quasiorderings and transgraphs, Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70TA106.


LINKS

Table of n, a(n) for n=0..15.
G. Brinkmann, B. D. McKay, Posets on up to 16 Points, Order 19 (2) (2002) 147179 (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) = 21/B(x), where B(x) is e.g.f. of A001035.  Vladeta Jovovic, Jan 10 2006


CROSSREFS

Cf. A046907.
Sequence in context: A003710 A027837 A174315 * A005014 A201063 A157035
Adjacent sequences: A046905 A046906 A046907 * A046909 A046910 A046911


KEYWORD

nonn


AUTHOR

John A. Wright.


EXTENSIONS

More terms from Vladeta Jovovic, Jan 10 2006


STATUS

approved



