Column k=3 of triangle A257673.

Terms

a(0) =1a(1) =9a(2) =45a(3) =174a(4) =576a(5) =1719a(6) =4761a(7) =12441a(8) =31050a(9) =74593a(10) =173547a(11) =392787a(12) =867876a(13) =1877322a(14) =3984636a(15) =8314434a(16) =17082510a(17) =34604523a(18) =69194309a(19) =136709688a(20) =267111510a(21) =516515227a(22) =989147760a(23) =1877103486a(24) =3531796959a(25) =6591644601a(26) =12208734552a(27) =22449066710a(28) =40995144288