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

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =12a(6) =32a(7) =82a(8) =208a(9) =528a(10) =1344a(11) =3428a(12) =8752a(13) =22352a(14) =57088a(15) =145800a(16) =372352a(17) =950912a(18) =2428416a(19) =6201616a(20) =15837504a(21) =40445376a(22) =103288320a(23) =263775008a(24) =673621760a(25) =1720277760a(26) =4393200640a(27) =11219241536a(28) =28651407104a(29) =73169217792