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 A275801 Number of alternating permutations of the multiset {1,1,2,2,...,n,n}. 4
 1, 0, 1, 4, 53, 936, 25325, 933980, 45504649, 2824517520, 217690037497, 20394614883316, 2282650939846781, 300814135522967736, 46103574973075123877, 8130996533576437261772, 1635028654501420083152785, 371853339350614571322913824, 94969025880924845123887493233 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Number of permutations (p(1),...,p(2n)) of {1,1,2,2,...,n,n} satisfying p(1) < p(2) > p(3) < ... < p(2n). a(n) <= A005799(n) <= A275829(n). LINKS Max Alekseyev, Table of n, a(n) for n = 0..70 Wikipedia, Alternating permutation. hkju et al., Number of updown sequences of 1,1,2,2,...,n,n, Mathoverflow, 2016. CROSSREFS Column k=2 of A275784. Cf. A000111, A001250, A000459, A004075, A005799, A114938, A137729, A137730, A137737, A137749, A275829. Sequence in context: A099340 A221605 A307172 * A158259 A095210 A156469 Adjacent sequences:  A275798 A275799 A275800 * A275802 A275803 A275804 KEYWORD nonn AUTHOR Max Alekseyev, Aug 09 2016 STATUS approved

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Last modified November 28 04:31 EST 2021. Contains 349400 sequences. (Running on oeis4.)