a(n) = floor(sqrt(5*2^n)).

Terms

a(0) =2a(1) =3a(2) =4a(3) =6a(4) =8a(5) =12a(6) =17a(7) =25a(8) =35a(9) =50a(10) =71a(11) =101a(12) =143a(13) =202a(14) =286a(15) =404a(16) =572a(17) =809a(18) =1144a(19) =1619a(20) =2289a(21) =3238a(22) =4579a(23) =6476a(24) =9158a(25) =12952a(26) =18317a(27) =25905a(28) =36635a(29) =51810