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

Terms

a(0) =1a(1) =3a(2) =12a(3) =44a(4) =144a(5) =432a(6) =1216a(7) =3264a(8) =8448a(9) =21248a(10) =52224a(11) =125952a(12) =299008a(13) =700416a(14) =1622016a(15) =3719168a(16) =8454144a(17) =19070976a(18) =42729472a(19) =95158272a(20) =210763776a(21) =464519168a(22) =1019215872a(23) =2227175424a(24) =4848615424a(25) =10519314432a(26) =22749904896a(27) =49056579584a(28) =105495134208a(29) =226291089408