%I #5 May 24 2014 18:27:21

%S 1,0,2,0,2,6,15,44,74,202,351,766,1301,2626,4677,8993,16466,31671,

%T 60266,116751,229180,452667,905627,1815394,3673666,7429123,15109955,

%U 30696510,62512866,127140993,258745131,525845884,1068309682,2167462318,4393853912,8896007640

%N Number of compositions of n with difference -1 between the number of odd parts and the number of even parts, both counted without multiplicity.

%H Alois P. Heinz, <a href="/A242840/b242840.txt">Table of n, a(n) for n = 2..500</a>

%e a(2) = 1: [2].

%e a(4) = 2: [2,2], [4].

%e a(6) = 2: [2,2,2], [6].

%e a(7) = 6: [1,2,4], [1,4,2], [2,1,4], [2,4,1], [4,1,2], [4,2,1].

%e a(8) = 15: [2,2,2,2], [1,1,2,4], [1,1,4,2], [1,2,1,4], [1,2,4,1], [1,4,1,2], [1,4,2,1], [2,1,1,4], [2,1,4,1], [2,4,1,1], [4,1,1,2], [4,1,2,1], [4,2,1,1], [4,4], [8].

%Y Column k=-1 of A242626.

%K nonn

%O 2,3

%A _Alois P. Heinz_, May 23 2014