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

Terms

a(0) =0a(1) =2a(2) =10a(3) =34a(4) =98a(5) =258a(6) =642a(7) =1538a(8) =3586a(9) =8194a(10) =18434a(11) =40962a(12) =90114a(13) =196610a(14) =425986a(15) =917506a(16) =1966082a(17) =4194306a(18) =8912898a(19) =18874370a(20) =39845890a(21) =83886082a(22) =176160770a(23) =369098754a(24) =771751938a(25) =1610612738a(26) =3355443202a(27) =6979321858a(28) =14495514626a(29) =30064771074