Column k=6 of triangle A257673.

Terms

a(0) =1a(1) =18a(2) =171a(3) =1158a(4) =6309a(5) =29466a(6) =122580a(7) =465738a(8) =1644516a(9) =5464892a(10) =17253369a(11) =52128540a(12) =151592391a(13) =426265836a(14) =1163373243a(15) =3091338000a(16) =8018585046a(17) =20348618814a(18) =50615278427a(19) =123608650182a(20) =296794147017a(21) =701525018576