a(n) = prime(2^(n+1)) - 2*prime(2^n).

Terms

a(0) =-1a(1) =1a(2) =5a(3) =15a(4) =25a(5) =49a(6) =97a(7) =181a(8) =433a(9) =819a(10) =1541a(11) =3147a(12) =6271a(13) =12469a(14) =25087a(15) =49455a(16) =99255a(17) =196057a(18) =391815a(19) =781893a(20) =1555935a(21) =3106511a(22) =6191001a(23) =12351963a(24) =24658715a(25) =49173803a(26) =98136735a(27) =195868789a(28) =391110307a(29) =780774507