Partial sums of the large Schroeder numbers (A006318).

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =121a(5) =515a(6) =2321a(7) =10879a(8) =52465a(9) =258563a(10) =1296281a(11) =6589727a(12) =33887465a(13) =175966211a(14) =921353249a(15) =4858956287a(16) =25786112993a(17) =137604139011a(18) =737922992937