a(n) is the largest prime < 4*a(n-1) for n > 1, with a(1) = 2.

Terms

a(0) =2a(1) =7a(2) =23a(3) =89a(4) =353a(5) =1409a(6) =5623a(7) =22483a(8) =89923a(9) =359663a(10) =1438643a(11) =5754571a(12) =23018273a(13) =92073083a(14) =368292317a(15) =1473169213a(16) =5892676849a(17) =23570707387a(18) =94282829533a(19) =377131318127