a(n) = 3*a(n-2) for n > 2; a(1) = 1; a(2) = 4.

Terms

a(0) =1a(1) =4a(2) =3a(3) =12a(4) =9a(5) =36a(6) =27a(7) =108a(8) =81a(9) =324a(10) =243a(11) =972a(12) =729a(13) =2916a(14) =2187a(15) =8748a(16) =6561a(17) =26244a(18) =19683a(19) =78732a(20) =59049a(21) =236196a(22) =177147a(23) =708588a(24) =531441a(25) =2125764a(26) =1594323a(27) =6377292a(28) =4782969a(29) =19131876