a(n) = n*4^(n/2 - 1)*(9 + (-1)^n).

Terms

a(0) =0a(1) =4a(2) =20a(3) =48a(4) =160a(5) =320a(6) =960a(7) =1792a(8) =5120a(9) =9216a(10) =25600a(11) =45056a(12) =122880a(13) =212992a(14) =573440a(15) =983040a(16) =2621440a(17) =4456448a(18) =11796480a(19) =19922944a(20) =52428800a(21) =88080384a(22) =230686720a(23) =385875968a(24) =1006632960a(25) =1677721600a(26) =4362076160a(27) =7247757312a(28) =18790481920a(29) =31138512896