%I A117514
%S A117514 1,1,2,18,248,5560,174752
%N 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).
%Y A117514 Cf. A002105, A117513, A117515.
%Y A117514 Sequence in context: A155666 A024486 A052635 this_sequence A138437 A121429 
               A109517
%Y A117514 Adjacent sequences: A117511 A117512 A117513 this_sequence A117515 A117516 
               A117517
%K A117514 nonn
%O A117514 1,3
%A A117514 Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006