A293498 - OEIS

A293498

Number of unlabeled semiorders on n points and having dimension at most 2.

1, 2, 5, 14, 42, 132, 426, 1390, 4544, 14822, 48183, 156118, 504487, 1627000, 5240019, 16861453, 54228190, 174351450, 560481708, 1801653769, 5791301311, 18615976402, 59841686254, 192366897839, 618392292337

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..25.

Mitchel T. Keller, Stephen J. Young, Hereditary Semiorders and Enumeration of Semiorders by Dimension, arXiv:1801.00501 [math.CO], 2018.

Index entries for linear recurrences with constant coefficients, signature (12,-61,172,-294,311,-197,66,-7).

FORMULA

G.f.: -x*(5*x^7 - 41*x^6 + 101*x^5 - 129*x^4 + 96*x^3 - 42*x^2 + 10*x - 1)/(7*x^8 - 66*x^7 + 197*x^6 - 311*x^5 + 294*x^4 - 172*x^3 + 61*x^2 - 12*x + 1).

CROSSREFS

Sequence in context: A261894 A287969 A061922 * A162746 A148329 A293499

Adjacent sequences: A293495 A293496 A293497 * A293499 A293500 A293501

KEYWORD

nonn,easy

AUTHOR

Mitchel T. Keller, Oct 10 2017

STATUS

approved

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