a(n) is least odd integer not a partial sum of 1, 3, ..., a(n-1).

Terms

a(0) =1a(1) =3a(2) =5a(3) =7a(4) =17a(5) =19a(6) =53a(7) =55a(8) =161a(9) =163a(10) =485a(11) =487a(12) =1457a(13) =1459a(14) =4373a(15) =4375a(16) =13121a(17) =13123a(18) =39365a(19) =39367a(20) =118097a(21) =118099a(22) =354293a(23) =354295a(24) =1062881a(25) =1062883a(26) =3188645a(27) =3188647a(28) =9565937a(29) =9565939