(5*F(n)+3*L(n)-8)/2.

Terms

a(0) =0a(1) =3a(2) =7a(3) =14a(4) =25a(5) =43a(6) =72a(7) =119a(8) =195a(9) =318a(10) =517a(11) =839a(12) =1360a(13) =2203a(14) =3567a(15) =5774a(16) =9345a(17) =15123a(18) =24472a(19) =39599a(20) =64075a(21) =103678a(22) =167757a(23) =271439a(24) =439200a(25) =710643a(26) =1149847a(27) =1860494a(28) =3010345a(29) =4870843