a(n) = 3*2^n + 2*n - 2.

Terms

a(0) =1a(1) =6a(2) =14a(3) =28a(4) =54a(5) =104a(6) =202a(7) =396a(8) =782a(9) =1552a(10) =3090a(11) =6164a(12) =12310a(13) =24600a(14) =49178a(15) =98332a(16) =196638a(17) =393248a(18) =786466a(19) =1572900a(20) =3145766a(21) =6291496a(22) =12582954a(23) =25165868a(24) =50331694a(25) =100663344a(26) =201326642a(27) =402653236a(28) =805306422a(29) =1610612792