a(0)=1, a(n) = 2*Fibonacci(n+4) - 6.

Terms

a(0) =1a(1) =4a(2) =10a(3) =20a(4) =36a(5) =62a(6) =104a(7) =172a(8) =282a(9) =460a(10) =748a(11) =1214a(12) =1968a(13) =3188a(14) =5162a(15) =8356a(16) =13524a(17) =21886a(18) =35416a(19) =57308a(20) =92730a(21) =150044a(22) =242780a(23) =392830a(24) =635616a(25) =1028452a(26) =1664074a(27) =2692532a(28) =4356612a(29) =7049150