a(n)=4a(n-2).

Terms

a(0) =12a(1) =21a(2) =48a(3) =84a(4) =192a(5) =336a(6) =768a(7) =1344a(8) =3072a(9) =5376a(10) =12288a(11) =21504a(12) =49152a(13) =86016a(14) =196608a(15) =344064a(16) =786432a(17) =1376256a(18) =3145728a(19) =5505024a(20) =12582912a(21) =22020096a(22) =50331648a(23) =88080384a(24) =201326592a(25) =352321536a(26) =805306368a(27) =1409286144a(28) =3221225472a(29) =5637144576