a(n) = 2*n * Stirling2(n-1,2).

Terms

a(0) =0a(1) =0a(2) =0a(3) =6a(4) =24a(5) =70a(6) =180a(7) =434a(8) =1008a(9) =2286a(10) =5100a(11) =11242a(12) =24552a(13) =53222a(14) =114660a(15) =245730a(16) =524256a(17) =1114078a(18) =2359260a(19) =4980698a(20) =10485720a(21) =22020054a(22) =46137300a(23) =96468946a(24) =201326544a(25) =419430350a(26) =872415180a(27) =1811939274a(28) =3758096328a(29) =7784628166