Column 1 of triangle A101494.

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =23a(5) =73a(6) =253a(7) =948a(8) =3817a(9) =16433a(10) =75295a(11) =365600a(12) =1874083a(13) =10108025a(14) =57194585a(15) =338615084a(16) =2092609701a(17) =13470059649a(18) =90137761867a(19) =625940219896