a(0) = 4; for n>0, a(n) = a(n-1) + 2^n - 3.

Terms

a(0) =4a(1) =3a(2) =4a(3) =9a(4) =22a(5) =51a(6) =112a(7) =237a(8) =490a(9) =999a(10) =2020a(11) =4065a(12) =8158a(13) =16347a(14) =32728a(15) =65493a(16) =131026a(17) =262095a(18) =524236a(19) =1048521a(20) =2097094a(21) =4194243a(22) =8388544a(23) =16777149a(24) =33554362a(25) =67108791a(26) =134217652a(27) =268435377a(28) =536870830a(29) =1073741739