a(n) = 2*a(n-1) + 4*a(n-2) with n>1, a(0)=0, a(1)=4.

Terms

a(0) =0a(1) =4a(2) =8a(3) =32a(4) =96a(5) =320a(6) =1024a(7) =3328a(8) =10752a(9) =34816a(10) =112640a(11) =364544a(12) =1179648a(13) =3817472a(14) =12353536a(15) =39976960a(16) =129368064a(17) =418643968a(18) =1354760192a(19) =4384096256a(20) =14187233280a(21) =45910851584a(22) =148570636288a(23) =480784678912