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

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =10a(5) =19a(6) =38a(7) =77a(8) =154a(9) =307a(10) =614a(11) =1229a(12) =2458a(13) =4915a(14) =9830a(15) =19661a(16) =39322a(17) =78643a(18) =157286a(19) =314573a(20) =629146a(21) =1258291a(22) =2516582a(23) =5033165a(24) =10066330a(25) =20132659a(26) =40265318a(27) =80530637a(28) =161061274a(29) =322122547