a(n) = 2*a(n-1) + 2*a(n-2) + 2*a(n-3) - a(n-4) with a(0)=0, a(1)=1, a(2)=4, a(3)=11.

Terms

a(0) =0a(1) =1a(2) =4a(3) =11a(4) =32a(5) =93a(6) =268a(7) =775a(8) =2240a(9) =6473a(10) =18708a(11) =54067a(12) =156256a(13) =451589a(14) =1305116a(15) =3771855a(16) =10900864a(17) =31504081a(18) =91048484a(19) =263135003a(20) =760474272a(21) =2197811437a(22) =6351792940a(23) =18357022295a(24) =53052779072a(25) =153325377177a(26) =443118564148