a(n) = 2^(n-2)*(3*binomial(n,3) + 6*binomial(n,2) + 6*n + 4).

Terms

a(0) =1a(1) =5a(2) =22a(3) =86a(4) =304a(5) =992a(6) =3040a(7) =8864a(8) =24832a(9) =67328a(10) =177664a(11) =458240a(12) =1159168a(13) =2883584a(14) =7069696a(15) =17113088a(16) =40960000a(17) =97058816a(18) =227934208a(19) =530972672a(20) =1227882496a(21) =2820669440a(22) =6440353792a(23) =14623440896a(24) =33034338304a(25) =74272735232a(26) =166262210560a(27) =370675810304a(28) =823291543552