a(n) = 3*a(n-1) -2*a(n-2) -a(n-3) +3*a(n-4) -2*a(n-5) for n > 4, with initial values as shown.

Terms

a(0) =0a(1) =1a(2) =2a(3) =2a(4) =4a(5) =9a(6) =21a(7) =43a(8) =86a(9) =170a(10) =340a(11) =681a(12) =1365a(13) =2731a(14) =5462a(15) =10922a(16) =21844a(17) =43689a(18) =87381a(19) =174763a(20) =349526a(21) =699050a(22) =1398100a(23) =2796201a(24) =5592405a(25) =11184811a(26) =22369622a(27) =44739242a(28) =89478484a(29) =178956969