a(n) = ((4+sqrt(5))*(1+sqrt(5))^n + (4-sqrt(5))*(1-sqrt(5))^n)/2.

Terms

a(0) =4a(1) =9a(2) =34a(3) =104a(4) =344a(5) =1104a(6) =3584a(7) =11584a(8) =37504a(9) =121344a(10) =392704a(11) =1270784a(12) =4112384a(13) =13307904a(14) =43065344a(15) =139362304a(16) =450985984a(17) =1459421184a(18) =4722786304a(19) =15283257344a(20) =49457659904a(21) =160048349184a(22) =517927337984