a(1) = 1; a(n) = nextprime(2*a(n-1)) for n > 1.

Terms

a(0) =1a(1) =3a(2) =7a(3) =17a(4) =37a(5) =79a(6) =163a(7) =331a(8) =673a(9) =1361a(10) =2729a(11) =5471a(12) =10949a(13) =21911a(14) =43853a(15) =87719a(16) =175447a(17) =350899a(18) =701819a(19) =1403641a(20) =2807303a(21) =5614657a(22) =11229331a(23) =22458671a(24) =44917381a(25) =89834777a(26) =179669557a(27) =359339171a(28) =718678369a(29) =1437356741