a(n+2) = 3*a(n), starting 4,7.

Terms

a(0) =4a(1) =7a(2) =12a(3) =21a(4) =36a(5) =63a(6) =108a(7) =189a(8) =324a(9) =567a(10) =972a(11) =1701a(12) =2916a(13) =5103a(14) =8748a(15) =15309a(16) =26244a(17) =45927a(18) =78732a(19) =137781a(20) =236196a(21) =413343a(22) =708588a(23) =1240029a(24) =2125764a(25) =3720087a(26) =6377292a(27) =11160261a(28) =19131876a(29) =33480783