The (2^n)-th lucky number.

Terms

a(0) =1a(1) =3a(2) =9a(3) =25a(4) =67a(5) =151a(6) =349a(7) =805a(8) =1831a(9) =4069a(10) =9063a(11) =19767a(12) =42975a(13) =92829a(14) =199123a(15) =425229a(16) =904225a(17) =1915381a(18) =4044235a(19) =8513505a(20) =17872759a(21) =37432615a(22) =78225409a(23) =163146639a(24) =339638307a(25) =705882493a(26) =1464816541a(27) =3035420871a(28) =6281814787a(29) =12984437515