a(n) = 3*Fibonacci(2*n) + 1.

Terms

a(0) =1a(1) =4a(2) =10a(3) =25a(4) =64a(5) =166a(6) =433a(7) =1132a(8) =2962a(9) =7753a(10) =20296a(11) =53134a(12) =139105a(13) =364180a(14) =953434a(15) =2496121a(16) =6534928a(17) =17108662a(18) =44791057a(19) =117264508a(20) =307002466a(21) =803742889a(22) =2104226200a(23) =5508935710a(24) =14422580929a(25) =37758807076a(26) =98853840298a(27) =258802713817a(28) =677554301152