a(n) = 2*a(n-1) + 7*a(n-2).

Terms

a(0) =1a(1) =9a(2) =25a(3) =113a(4) =401a(5) =1593a(6) =5993a(7) =23137a(8) =88225a(9) =338409a(10) =1294393a(11) =4957649a(12) =18976049a(13) =72655641a(14) =278143625a(15) =1064876737a(16) =4076758849a(17) =15607654857a(18) =59752621657a(19) =228758827313a(20) =875786006225