a(n) = (2^prime(n) - 8)/24 for n>=2.

Terms

a(0) =0a(1) =1a(2) =5a(3) =85a(4) =341a(5) =5461a(6) =21845a(7) =349525a(8) =22369621a(9) =89478485a(10) =5726623061a(11) =91625968981a(12) =366503875925