a(n) = largest prime <= 2a(n-1), with a(0)=1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =7a(5) =13a(6) =23a(7) =43a(8) =83a(9) =163a(10) =317a(11) =631a(12) =1259a(13) =2503a(14) =5003a(15) =9973a(16) =19937a(17) =39869a(18) =79699a(19) =159389a(20) =318751a(21) =637499a(22) =1274989a(23) =2549951a(24) =5099893a(25) =10199767a(26) =20399531a(27) =40799041a(28) =81598067a(29) =163196129