68923172032domain: NAppears in sequencesNumber of reversible strings with n-1 black beads and n-1 white beads. String is not palindromic.at n=20A032095a(n) = (1/2)*(binomial(4*n, 2*n) - (-1)^n*binomial(2*n,n)).at n=10A037964a(n) = Sum_{k=0..n} C(n,k)^2*mod(k,2).at n=20A110145