52221domain: NAppears in sequencesThe ninth Euler transform of the sequence with g.f. 1+x.at n=7A290358Number of 7-leaf rooted trees with n levels.at n=9A290361a(n) = 2*a(n-1) + 2*a(n-3) + a(n-4), with a(0) = 0 = a(1), a(2) = 2, and a(3) = 1.at n=15A353581a(n) = Sum_{k=0..floor(n/3)} binomial(3*n-3*k-2,n-3*k).at n=7A390705