a(n) = A151723(2^n).

Terms

a(0) =1a(1) =7a(2) =31a(3) =127a(4) =499a(5) =1975a(6) =7855a(7) =31327a(8) =125119a(9) =500083a(10) =1999507a(11) =7996327a(12) =31981903a(13) =127920955a(14) =511670911