a(n) = T(3,n), array T given by A048471.

Terms

a(0) =1a(1) =9a(2) =33a(3) =105a(4) =321a(5) =969a(6) =2913a(7) =8745a(8) =26241a(9) =78729a(10) =236193a(11) =708585a(12) =2125761a(13) =6377289a(14) =19131873a(15) =57395625a(16) =172186881a(17) =516560649a(18) =1549681953a(19) =4649045865a(20) =13947137601a(21) =41841412809a(22) =125524238433a(23) =376572715305