a(n) = a(n-1) + a(n-2) + 1, with a(0)=3, a(1)=8.

Terms

a(0) =3a(1) =8a(2) =12a(3) =21a(4) =34a(5) =56a(6) =91a(7) =148a(8) =240a(9) =389a(10) =630a(11) =1020a(12) =1651a(13) =2672a(14) =4324a(15) =6997a(16) =11322a(17) =18320a(18) =29643a(19) =47964a(20) =77608a(21) =125573a(22) =203182a(23) =328756a(24) =531939a(25) =860696a(26) =1392636a(27) =2253333a(28) =3645970a(29) =5899304