a(n) = 3*a(n-1) + 4*a(n-2), a(0)=a(1)=1.

Terms

a(0) =1a(1) =1a(2) =7a(3) =25a(4) =103a(5) =409a(6) =1639a(7) =6553a(8) =26215a(9) =104857a(10) =419431a(11) =1677721a(12) =6710887a(13) =26843545a(14) =107374183a(15) =429496729a(16) =1717986919a(17) =6871947673a(18) =27487790695a(19) =109951162777a(20) =439804651111