Generalized Jacobsthal numbers.

Terms

a(0) =0a(1) =1a(2) =5a(3) =11a(4) =25a(5) =51a(6) =105a(7) =211a(8) =425a(9) =851a(10) =1705a(11) =3411a(12) =6825a(13) =13651a(14) =27305a(15) =54611a(16) =109225a(17) =218451a(18) =436905a(19) =873811a(20) =1747625a(21) =3495251a(22) =6990505a(23) =13981011a(24) =27962025a(25) =55924051a(26) =111848105a(27) =223696211a(28) =447392425a(29) =894784851