6637879domain: NAppears in sequencesNumber of equivalence classes of ballot paths of length n for the string ddu.at n=44A274112Number of equivalence classes of Dyck paths of semilength n for the string duu.at n=23A274115a(n) = Sum_{k=0..n} (4*k+1) * binomial(2*n+2*k+1,n-k)/(2*n+2*k+1).at n=11A390527