a(n)=4a(n-2). Also 3*A084221.

Terms

a(0) =3a(1) =9a(2) =12a(3) =36a(4) =48a(5) =144a(6) =192a(7) =576a(8) =768a(9) =2304a(10) =3072a(11) =9216a(12) =12288a(13) =36864a(14) =49152a(15) =147456a(16) =196608a(17) =589824a(18) =786432a(19) =2359296a(20) =3145728a(21) =9437184a(22) =12582912a(23) =37748736a(24) =50331648a(25) =150994944a(26) =201326592a(27) =603979776a(28) =805306368a(29) =2415919104