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

Terms

a(0) =0a(1) =4a(2) =8a(3) =24a(4) =64a(5) =176a(6) =480a(7) =1312a(8) =3584a(9) =9792a(10) =26752a(11) =73088a(12) =199680a(13) =545536a(14) =1490432a(15) =4071936a(16) =11124736a(17) =30393344a(18) =83036160a(19) =226859008a(20) =619790336a(21) =1693298688a(22) =4626178048a(23) =12638953472a(24) =34530263040