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

Terms

a(0) =1a(1) =3a(2) =4a(3) =5a(4) =8a(5) =17a(6) =40a(7) =93a(8) =208a(9) =449a(10) =944a(11) =1949a(12) =3976a(13) =8049a(14) =16216a(15) =32573a(16) =65312a(17) =130817a(18) =261856a(19) =523965a(20) =1048216a(21) =2096753a(22) =4193864a(23) =8388125a(24) =16776688a(25) =33553857a(26) =67108240a(27) =134217053a(28) =268434728a(29) =536870129