a(n) = a(n-1) + a(n-2) + 1, with a(0) = 1 and a(1) = 4.

Terms

a(0) =1a(1) =4a(2) =6a(3) =11a(4) =18a(5) =30a(6) =49a(7) =80a(8) =130a(9) =211a(10) =342a(11) =554a(12) =897a(13) =1452a(14) =2350a(15) =3803a(16) =6154a(17) =9958a(18) =16113a(19) =26072a(20) =42186a(21) =68259a(22) =110446a(23) =178706a(24) =289153a(25) =467860a(26) =757014a(27) =1224875a(28) =1981890a(29) =3206766