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A279573
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Number of length n inversion sequences avoiding the patterns 120 and 210.
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23
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1, 1, 2, 6, 23, 102, 499, 2625, 14601, 84847, 510614, 3161964, 20050770, 129718404, 853689031, 5701759424, 38574689104, 263936457042, 1824032887177, 12718193293888, 89386742081688, 632746535420834, 4508140253686638, 32308561883462867, 232790342330880572
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OFFSET
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0,3
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COMMENTS
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A length n inversion sequence e_1e_2...e_n is a sequence of integers where 0 <= e_i <= i-1. The term a(n) counts those length n inversion sequences with no entries e_i, e_j, e_k (where i<j<k) such that e_i <> e_j > e_k and e_i > e_k. This is the same as the set of length n inversion sequences avoiding 120 and 210.
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LINKS
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FORMULA
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a(n) ~ c * 8^n / n^(3/2), where c = 0.0013548789253263217919... - Vaclav Kotesovec, Oct 07 2021
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EXAMPLE
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The length 4 inversion sequences avoiding (120,210) are 0000, 0001, 0002, 0003, 0010, 0011, 0012, 0013, 0020, 0021, 0022, 0023, 0100, 0101, 0102, 0103, 0110, 0111, 0112, 0113, 0121, 0122, 0123.
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CROSSREFS
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Cf. A000108, A057552, A263777, A263778, A263779, A263780, A279551, A279552, A279553, A279554, A279555, A279556, A279557, A279558, A279559, A279560, A279561, A279562, A279563, A279564, A279565, A279566, A279567, A279568, A279569, A279570, A279571, A279572.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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