a(n) = 23*2^n - 1.

Terms

a(0) =22a(1) =45a(2) =91a(3) =183a(4) =367a(5) =735a(6) =1471a(7) =2943a(8) =5887a(9) =11775a(10) =23551a(11) =47103a(12) =94207a(13) =188415a(14) =376831a(15) =753663a(16) =1507327a(17) =3014655a(18) =6029311a(19) =12058623a(20) =24117247a(21) =48234495a(22) =96468991a(23) =192937983a(24) =385875967a(25) =771751935a(26) =1543503871a(27) =3087007743a(28) =6174015487a(29) =12348030975