A trisection of A161804: a(n) = A161804(3n+2) for n>=0.

Terms

a(0) =3a(1) =27a(2) =111a(3) =378a(4) =1356a(5) =4131a(6) =10881a(7) =29106a(8) =73500a(9) =167643a(10) =382053a(11) =849339a(12) =1754061a(13) =3605094a(14) =7330311a(15) =14094945a(16) =26980563a(17) =51481332a(18) =93965784a(19) =170910270a(20) =311155296a(21) =545970024a(22) =955201653a(23) =1676274750a(24) =2849709768a(25) =4831999623