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

Terms

a(0) =1a(1) =2a(2) =9a(3) =30a(4) =109a(5) =386a(6) =1377a(7) =4902a(8) =17461a(9) =62186a(10) =221481a(11) =788814a(12) =2809405a(13) =10005842a(14) =35636337a(15) =126920694a(16) =452034757a(17) =1609945658a(18) =5733906489a(19) =20421610782a(20) =72732645325a(21) =259041157538a(22) =922588763265