Column k=4 of triangle A257673.

Terms

a(0) =1a(1) =12a(2) =78a(3) =376a(4) =1509a(5) =5340a(6) =17234a(7) =51796a(8) =147054a(9) =398388a(10) =1037560a(11) =2612520a(12) =6387965a(13) =15221412a(14) =35446980a(15) =80865304a(16) =181076216a(17) =398660292a(18) =864186408a(19) =1846759404a(20) =3894731430a(21) =8113669352a(22) =16710519860a(23) =34049851236a(24) =68687627812a(25) =137257430140a(26) =271842916654