300546630domain: NAppears in sequencesNumber of 2n-bead black-white reversible strings with n black beads.at n=16A032123Central column of Losanitsch's triangle A034851.at n=32A034872a(n) = Sum_{k=0..n} binomial(2*n,2*k)^2.at n=8A098772Number of n-element subsets of [2n] having an even sum.at n=16A119358