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

Terms

a(0) =3a(1) =2a(2) =5a(3) =10a(4) =25a(5) =56a(6) =128a(7) =288a(8) =649a(9) =1459a(10) =3280a(11) =7371a(12) =16564a(13) =37220a(14) =83634a(15) =187925a(16) =422265a(17) =948822a(18) =2131985a(19) =4790528a(20) =10764220a(21) =24186984a(22) =54347661a(23) =122118087a(24) =274396852a(25) =616564131