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

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =6a(5) =29a(6) =161a(7) =928a(8) =5388a(9) =31333a(10) =182269a(11) =1060358a(12) =6168762a(13) =35887625a(14) =208781333a(15) =1214615068a(16) =7066195896a(17) =41108599753a(18) =239155126777