a(n) = a(n-1) + a(n-2) + 1, with a(0) = 0 and a(1) = 12.

Terms

a(0) =0a(1) =12a(2) =13a(3) =26a(4) =40a(5) =67a(6) =108a(7) =176a(8) =285a(9) =462a(10) =748a(11) =1211a(12) =1960a(13) =3172a(14) =5133a(15) =8306a(16) =13440a(17) =21747a(18) =35188a(19) =56936a(20) =92125a(21) =149062a(22) =241188a(23) =390251a(24) =631440a(25) =1021692a(26) =1653133a(27) =2674826a(28) =4327960a(29) =7002787