A117514 - OEIS

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A117514

Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that the first token is a 1 and between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n).

%I #2 Feb 27 2009 03:00:00

%S 1,1,2,18,248,5560,174752

%N Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that the first token is a 1 and between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n).

%Y Cf. A002105, A117513, A117515.

%K nonn

%O 1,3

%A Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006