Generalized Jacobsthal sequence.

Terms

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