Column 4 of triangle A055898.

Terms

a(0) =1a(1) =9a(2) =51a(3) =209a(4) =696a(5) =1980a(6) =5000a(7) =11475a(8) =24375a(9) =48545a(10) =91581a(11) =164934a(12) =285376a(13) =476784a(14) =772416a(15) =1217610a(16) =1873125a(17) =2819025a(18) =4159375a(19) =6027615a(20) =8592936a(21) =12067484a(22) =16714776a(23) =22859109a(24) =30896411a(25) =41306265a(26) =54665625a(27) =71663900