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

Terms

a(0) =0a(1) =1a(2) =2a(3) =11a(4) =36a(5) =149a(6) =550a(7) =2143a(8) =8136a(9) =31273a(10) =119498a(11) =457907a(12) =1752300a(13) =6709949a(14) =25685998a(15) =98341639a(16) =376485264a(17) =1441362001a(18) =5518120850a(19) =21125775707a(20) =80878397364a(21) =309637224677