A117515 - cp's OEIS frontend

A117515 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).

%I A117515 #1 May 19 2006 03:00:00
%S A117515 1,2,6,72,1240,33360
%N A117515 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 A117515 Cf. A002105, A117514, A117513.
%K A117515 nonn
%O A117515 1,2
%A A117515 Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006

cp's OEIS Frontend

A117515 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).