Column k=7 of triangle A257673.

Terms

a(0) =1a(1) =21a(2) =231a(3) =1792a(4) =11067a(5) =58044a(6) =268940a(7) =1129999a(8) =4385136a(9) =15928948a(10) =54711958a(11) =179090772a(12) =562156203a(13) =1700628930a(14) =4978677738a(15) =14153099499a(16) =39180254316a(17) =105881154624a(18) =279906223856a(19) =725158329175