A generalized Jacobsthal sequence.

Terms

a(0) =3a(1) =5a(2) =13a(3) =25a(4) =53a(5) =105a(6) =213a(7) =425a(8) =853a(9) =1705a(10) =3413a(11) =6825a(12) =13653a(13) =27305a(14) =54613a(15) =109225a(16) =218453a(17) =436905a(18) =873813a(19) =1747625a(20) =3495253a(21) =6990505a(22) =13981013a(23) =27962025a(24) =55924053a(25) =111848105a(26) =223696213a(27) =447392425a(28) =894784853a(29) =1789569705