9051563520domain: NAppears in sequencesa(n) = n * binomial(2*n, n-1).at n=16A110609a(n) = x(n) * 2^((n mod 2 - 1)/2), with x(n)=Sum(x(k)*x(n-k-1):0<=k<n), x(0)=SQRT(2).at n=16A137697Number of valleys in all left factors of Dyck paths of length n. A valley is a (1,-1)-step followed by a (1,1)-step.at n=33A191522