a(0)=1, a(n)= 2+2^n/6+4*(-1)^n/3, n>0.

Terms

a(0) =1a(1) =1a(2) =4a(3) =2a(4) =6a(5) =6a(6) =14a(7) =22a(8) =46a(9) =86a(10) =174a(11) =342a(12) =686a(13) =1366a(14) =2734a(15) =5462a(16) =10926a(17) =21846a(18) =43694a(19) =87382a(20) =174766a(21) =349526a(22) =699054a(23) =1398102a(24) =2796206a(25) =5592406a(26) =11184814a(27) =22369622a(28) =44739246a(29) =89478486