A003431 Number of isomorphism classes of connected irreducible posets with n labeled points.

1, 1, 0, 0, 1, 12, 104, 956, 10037, 126578, 1971005, 38569954, 958347642, 30400603560, 1234260982770, 64187360439352, 4275470549123119

Offset: 0

Author

N. J. A. Sloane and Richard Stanley

Keywords

• nonn
• nice
• more

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• S. R. Finch, Series-parallel networks
• S. R. Finch, Series-parallel networks, July 7, 2003. [Cached copy, with permission of the author]
• R. P. Stanley, Enumeration of posets generated by disjoint unions and ordinal sums, Proc. Amer. Math. Soc. 45 (1974), 295-299.
• R. P. Stanley, Letter to N. J. A. Sloane, c. 1991
• J. A. Wright, Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences
• Index entries for sequences related to posets

Crossrefs

Cf. A003430, A046906.

Extensions

More terms from Richard Stanley, Jun 19 2003

2 more terms from Vladeta Jovovic, Feb 17 2008

Title clarified by Geoffrey Critzer, Jul 08 2022

a(0) changed to 1 by Geoffrey Critzer, Jul 10 2022