G.f. satisfies: A(x) = 1/(1-x) - 1/(1-x*A(x)) + 1/(1-x*A(x)^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =23a(5) =98a(6) =440a(7) =2044a(8) =9742a(9) =47384a(10) =234289a(11) =1174214a(12) =5951877a(13) =30459550a(14) =157168265a(15) =816777857a(16) =4271248777a(17) =22459464722a(18) =118678530165a(19) =629867928597