a(n) = 3*Fibonacci(2*n) + 0^n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =24a(4) =63a(5) =165a(6) =432a(7) =1131a(8) =2961a(9) =7752a(10) =20295a(11) =53133a(12) =139104a(13) =364179a(14) =953433a(15) =2496120a(16) =6534927a(17) =17108661a(18) =44791056a(19) =117264507a(20) =307002465a(21) =803742888a(22) =2104226199a(23) =5508935709a(24) =14422580928a(25) =37758807075a(26) =98853840297a(27) =258802713816