a(n) = 2^(n-1)*(2^n+7).

Terms

a(0) =4a(1) =9a(2) =22a(3) =60a(4) =184a(5) =624a(6) =2272a(7) =8640a(8) =33664a(9) =132864a(10) =527872a(11) =2104320a(12) =8402944a(13) =33583104a(14) =134275072a(15) =536985600a(16) =2147713024a(17) =8590393344a(18) =34360655872a(19) =137440788480a(20) =549759483904