a(n) = 4*a(n-1) -5*a(n-2) +2*a(n-3) +2*a(n-4) for a(0) = a(1) = 0, a(2) = 1, a(3) = 4 for n >= 4.

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =11a(5) =26a(6) =59a(7) =136a(8) =323a(9) =782a(10) =1903a(11) =4620a(12) =11175a(13) =26970a(14) =65051a(15) =156944a(16) =378811a(17) =914566a(18) =2208199a(19) =5331476a(20) =12871663a(21) =31074802a(22) =75020243a(23) =181113240a(24) =437244675a(25) =1055602590a(26) =2548453951a(27) =6152518684a(28) =14853499511a(29) =35859517706