Column 2 of triangle A117418.

Terms

a(0) =1a(1) =3a(2) =8a(3) =22a(4) =65a(5) =208a(6) =723a(7) =2721a(8) =11053a(9) =48220a(10) =224548a(11) =1109098a(12) =5778541a(13) =31599829a(14) =180605494a(15) =1074867617a(16) =6641877097a(17) =42500291653a(18) =280917956733