A007318 * A000125.

Terms

a(0) =1a(1) =3a(2) =9a(3) =27a(4) =80a(5) =232a(6) =656a(7) =1808a(8) =4864a(9) =12800a(10) =33024a(11) =83712a(12) =208896a(13) =514048a(14) =1249280a(15) =3002368a(16) =7143424a(17) =16842752a(18) =39387136a(19) =91422720a(20) =210763776a(21) =482869248a(22) =1099956224a(23) =2492465152a(24) =5620367360a(25) =12616466432a(26) =28202500096a(27) =62797119488a(28) =139318001664a(29) =308029685760