a(n) = 2^prime(n)-prime(n).

Terms

a(0) =2a(1) =5a(2) =27a(3) =121a(4) =2037a(5) =8179a(6) =131055a(7) =524269a(8) =8388585a(9) =536870883a(10) =2147483617a(11) =137438953435