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A275829
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Number of weakly alternating permutations of the multiset {1,1,2,2,...,n,n}.
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3
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1, 1, 2, 12, 140, 2564, 68728, 2539632, 123686800, 7677924688, 591741636128, 55438330474944, 6204888219697856, 817697605612952384, 125322509904814743424, 22102340129003429880576, 4444468680409243484516608, 1010802175212828388101900544, 258152577318424951261637001728
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OFFSET
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0,3
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COMMENTS
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Number of permutations (p(1),...,p(2n)) of {1,1,2,2,...,n,n} satisfying p(1) <= p(2) >= p(3) <= p(4) >= p(5) <= ... <= p(2n).
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LINKS
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CROSSREFS
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Cf. A000111, A001250, A000459, A004075, A005799, A114938, A137729, A137730, A137737, A137749, A275801.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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