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A293498 Number of unlabeled semiorders on n points and having dimension at most 2. 1
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 (list; graph; refs; listen; history; text; internal format)
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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Last modified December 10 12:43 EST 2019. Contains 329896 sequences. (Running on oeis4.)