a(n) = sqrt(A137880(n)).

Terms

a(0) =1a(1) =7a(2) =15a(3) =153a(4) =329a(5) =3359a(6) =7223a(7) =73745a(8) =158577a(9) =1619031a(10) =3481471a(11) =35544937a(12) =76433785a(13) =780369583a(14) =1678061799a(15) =17132585889a(16) =36840925793a(17) =376136519975a(18) =808822305647