Generalized Catalan numbers C(3; n).

Terms

a(0) =1a(1) =1a(2) =4a(3) =25a(4) =190a(5) =1606a(6) =14506a(7) =137089a(8) =1338790a(9) =13403950a(10) =136846144a(11) =1419257434a(12) =14911016596a(13) =158363649640