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
Offset: 1
Links
- 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).