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%I #1 May 19 2006 03:00:00
%S 1,2,6,72,1240,33360
%N Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n).
%Y Cf. A002105, A117514, A117513.
%K nonn
%O 1,2
%A Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006
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