Column 1 of triangle A128567.

Terms

a(0) =1a(1) =6a(2) =31a(3) =133a(4) =587a(5) =2531a(6) =10950a(7) =47185a(8) =203704a(9) =879711a(10) =3804530a(11) =16464710a(12) =71312805a(13) =309083291a(14) =1340546867a(15) =5817555402a(16) =25258769216a(17) =109711224970a(18) =476675868834