a(n) = 2*Fibonacci(n) - (1 - (-1)^n)/2.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =9a(6) =16a(7) =25a(8) =42a(9) =67a(10) =110a(11) =177a(12) =288a(13) =465a(14) =754a(15) =1219a(16) =1974a(17) =3193a(18) =5168a(19) =8361a(20) =13530a(21) =21891a(22) =35422a(23) =57313a(24) =92736a(25) =150049a(26) =242786a(27) =392835a(28) =635622a(29) =1028457