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%I #6 Sep 08 2016 08:35:10
%S 1,0,1,12,761,87336,18528505,6376563600,3338759427857,
%T 2524750777586976,2648982517454387281,3733860677541032881728,
%U 6885982148044369769847497,16251753910337100552968630400
%N Number of up-down sequences with 3 copies each of 1,2,...,n.
%e a(3) = 12: 121313232, 121323132, 121323231, 131213232, 132312132, 132323121, 231213132, 231213231, 231312132, 231323121, 232312131, 232313121.
%e a(4) = 761: 121213243434, 121214343423, 121313242434, 121313243424, ..., 343424121213, 343424121312, 343424131212, 343434121212.
%Y Column k=3 of A275784.
%K nonn
%O 0,4
%A _Alois P. Heinz_, Sep 08 2016
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