a(n) = 2*a(n-1) + 2*a(n-2) - 4*a(n-3) with n>2, a(0)=0, a(1)=1, a(2)=3.

Terms

a(0) =0a(1) =1a(2) =3a(3) =8a(4) =18a(5) =40a(6) =84a(7) =176a(8) =360a(9) =736a(10) =1488a(11) =3008a(12) =6048a(13) =12160a(14) =24384a(15) =48896a(16) =97920a(17) =196096a(18) =392448a(19) =785408a(20) =1571328a(21) =3143680a(22) =6288384a(23) =12578816a(24) =25159680a(25) =50323456a(26) =100651008a(27) =201310208a(28) =402628608a(29) =805273600