a(n) = a(n-1) + 2*a(n-2) with a(0)=0, a(1)=2.

Terms

a(0) =0a(1) =2a(2) =2a(3) =6a(4) =10a(5) =22a(6) =42a(7) =86a(8) =170a(9) =342a(10) =682a(11) =1366a(12) =2730a(13) =5462a(14) =10922a(15) =21846a(16) =43690a(17) =87382a(18) =174762a(19) =349526a(20) =699050a(21) =1398102a(22) =2796202a(23) =5592406a(24) =11184810a(25) =22369622a(26) =44739242a(27) =89478486a(28) =178956970a(29) =357913942