a(n) = 3*a(n-1) if n is odd, otherwise 6*a(n-1).

Terms

a(0) =1a(1) =3a(2) =18a(3) =54a(4) =324a(5) =972a(6) =5832a(7) =17496a(8) =104976a(9) =314928a(10) =1889568a(11) =5668704a(12) =34012224a(13) =102036672a(14) =612220032a(15) =1836660096a(16) =11019960576a(17) =33059881728a(18) =198359290368a(19) =595077871104