2^p - 11 for p prime.

Terms

a(0) =-7a(1) =-3a(2) =21a(3) =117a(4) =2037a(5) =8181a(6) =131061a(7) =524277a(8) =8388597a(9) =536870901a(10) =2147483637a(11) =137438953461