a(0)=1; a(n) = 2*3^(n-1) for n >= 1.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =54a(5) =162a(6) =486a(7) =1458a(8) =4374a(9) =13122a(10) =39366a(11) =118098a(12) =354294a(13) =1062882a(14) =3188646a(15) =9565938a(16) =28697814a(17) =86093442a(18) =258280326a(19) =774840978a(20) =2324522934a(21) =6973568802a(22) =20920706406a(23) =62762119218a(24) =188286357654a(25) =564859072962