a(n) = a(n-1) + a(n-2) + 1 for n>1, a(0)=3, a(1)=11.

Terms

a(0) =3a(1) =11a(2) =15a(3) =27a(4) =43a(5) =71a(6) =115a(7) =187a(8) =303a(9) =491a(10) =795a(11) =1287a(12) =2083a(13) =3371a(14) =5455a(15) =8827a(16) =14283a(17) =23111a(18) =37395a(19) =60507a(20) =97903a(21) =158411a(22) =256315a(23) =414727a(24) =671043a(25) =1085771a(26) =1756815a(27) =2842587a(28) =4599403a(29) =7441991