a(n) = 2^(n-3)*(n + 3)*(2*n - 3).

Terms

a(0) =18a(1) =70a(2) =224a(3) =648a(4) =1760a(5) =4576a(6) =11520a(7) =28288a(8) =68096a(9) =161280a(10) =376832a(11) =870400a(12) =1990656a(13) =4513792a(14) =10158080a(15) =22708224a(16) =50462720a(17) =111542272a(18) =245366784a(19) =537395200a(20) =1172307968a(21) =2548039680a(22) =5519704064a(23) =11920211968a(24) =25669140480a(25) =55129931776a(26) =118111600640a(27) =252463546368a(28) =538481524736