a(n) = 8*a(n-2) for n > 2; a(1) = 5, a(2) = 12.

Terms

a(0) =5a(1) =12a(2) =40a(3) =96a(4) =320a(5) =768a(6) =2560a(7) =6144a(8) =20480a(9) =49152a(10) =163840a(11) =393216a(12) =1310720a(13) =3145728a(14) =10485760a(15) =25165824a(16) =83886080a(17) =201326592a(18) =671088640a(19) =1610612736a(20) =5368709120a(21) =12884901888a(22) =42949672960a(23) =103079215104a(24) =343597383680a(25) =824633720832