a(n) = 247*2^n - 300.

Terms

a(0) =194a(1) =688a(2) =1676a(3) =3652a(4) =7604a(5) =15508a(6) =31316a(7) =62932a(8) =126164a(9) =252628a(10) =505556a(11) =1011412a(12) =2023124a(13) =4046548a(14) =8093396a(15) =16187092a(16) =32374484a(17) =64749268a(18) =129498836a(19) =258997972a(20) =517996244a(21) =1035992788a(22) =2071985876a(23) =4143972052a(24) =8287944404a(25) =16575889108a(26) =33151778516a(27) =66303557332