4537543340domain: NAppears in sequencesNumber of reversible strings with n-1 black beads and n-1 white beads. String is not palindromic.at n=18A032095a(n) = Sum_{k=0..n} binomial(2*n,2*k)^2.at n=9A098772Number of n-element subsets of [2n] having an even sum.at n=18A119358