a(n) = (1/2)*A291730(n).

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =84a(5) =255a(6) =772a(7) =2340a(8) =7088a(9) =21476a(10) =65064a(11) =197126a(12) =597228a(13) =1809420a(14) =5481980a(15) =16608712a(16) =50319264a(17) =152451844a(18) =461882016a(19) =1399359936a(20) =4239628608a(21) =12844765920a(22) =38915675520a(23) =117902483528a(24) =357208128400