a(n) = 2*a(n-1) + 7*a(n-2) for n>1, a(0)=1, a(1)=1.

Terms

a(0) =1a(1) =1a(2) =9a(3) =25a(4) =113a(5) =401a(6) =1593a(7) =5993a(8) =23137a(9) =88225a(10) =338409a(11) =1294393a(12) =4957649a(13) =18976049a(14) =72655641a(15) =278143625a(16) =1064876737a(17) =4076758849a(18) =15607654857a(19) =59752621657a(20) =228758827313a(21) =875786006225