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

Terms

a(0) =2a(1) =6a(2) =24a(3) =88a(4) =288a(5) =864a(6) =2432a(7) =6528a(8) =16896a(9) =42496a(10) =104448a(11) =251904a(12) =598016a(13) =1400832a(14) =3244032a(15) =7438336a(16) =16908288a(17) =38141952a(18) =85458944a(19) =190316544a(20) =421527552a(21) =929038336a(22) =2038431744a(23) =4454350848a(24) =9697230848a(25) =21038628864a(26) =45499809792a(27) =98113159168a(28) =210990268416