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%I #8 Aug 12 2016 15:37:55
%S 1,1,2,12,140,2564,68728,2539632,123686800,7677924688,591741636128,
%T 55438330474944,6204888219697856,817697605612952384,
%U 125322509904814743424,22102340129003429880576,4444468680409243484516608,1010802175212828388101900544,258152577318424951261637001728
%N Number of weakly alternating permutations of the multiset {1,1,2,2,...,n,n}.
%C 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).
%C a(n) >= A005799(n) >= A275801(n).
%H Max Alekseyev, <a href="/A275829/b275829.txt">Table of n, a(n) for n = 0..70</a>
%Y Cf. A000111, A001250, A000459, A004075, A005799, A114938, A137729, A137730, A137737, A137749, A275801.
%K nonn
%O 0,3
%A _Max Alekseyev_, Aug 11 2016