a(n) = (1/2)*A290904(n).

Terms

a(0) =0a(1) =1a(2) =4a(3) =12a(4) =36a(5) =111a(6) =344a(7) =1064a(8) =3288a(9) =10161a(10) =31404a(11) =97060a(12) =299980a(13) =927135a(14) =2865456a(15) =8856144a(16) =27371312a(17) =84595361a(18) =261455316a(19) =808068924a(20) =2497464564a(21) =7718808463a(22) =23856195976a(23) =73731339384a(24) =227878342920a(25) =704293989585