a(n) = 2*a(n-1) + a(n-2) - a(n-3) + a(n-4), with a(1) = 0, a(2) = 3, a(3) = 5 and a(4) = 17.

Terms

a(0) =0a(1) =3a(2) =5a(3) =17a(4) =36a(5) =87a(6) =198a(7) =464a(8) =1075a(9) =2503a(10) =5815a(11) =13522a(12) =31431a(13) =73072a(14) =169868a(15) =394899a(16) =918025a(17) =2134153a(18) =4961300a(19) =11533627a(20) =26812426a(21) =62331332a(22) =144902763a(23) =336858059a(24) =783099975a(25) =1820486578a(26) =4232117835a(27) =9838480332a(28) =22871691896a(29) =53170232867