a(n)= 3*a(n-1) -3*a(n-3) +a(n-4), n>6.

Terms

a(0) =1a(1) =1a(2) =1a(3) =0a(4) =4a(5) =8a(6) =25a(7) =63a(8) =169a(9) =440a(10) =1156a(11) =3024a(12) =7921a(13) =20735a(14) =54289a(15) =142128a(16) =372100a(17) =974168a(18) =2550409a(19) =6677055a(20) =17480761a(21) =45765224a(22) =119814916a(23) =313679520a(24) =821223649a(25) =2149991423a(26) =5628750625a(27) =14736260448a(28) =38580030724a(29) =101003831720