Column 2 of triangle A123305.

Terms

a(0) =1a(1) =3a(2) =18a(3) =144a(4) =1422a(5) =16848a(6) =235458a(7) =3827628a(8) =71466174a(9) =1515031920a(10) =36091609434a(11) =957367079244