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A293498
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Number of unlabeled semiorders on n points and having dimension at most 2.
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1
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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
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1,2
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LINKS
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FORMULA
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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).
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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