A trisection of A161804: a(n) = A161804(3n+1) for n>=0.

Terms

a(0) =3a(1) =30a(2) =141a(3) =513a(4) =1815a(5) =5727a(6) =15882a(7) =42417a(8) =108165a(9) =255831a(10) =585258a(11) =1302966a(12) =2762349a(13) =5705829a(14) =11577633a(15) =22708053a(16) =43675938a(17) =83011398a(18) =153929484a(19) =281210994a(20) =509494515a(21) =905832642a(22) =1591395774a(23) =2778237765a(24) =4776943011