a(n) is the largest square with n binary digits.

Terms

a(0) =4a(1) =9a(2) =25a(3) =49a(4) =121a(5) =225a(6) =484a(7) =961a(8) =2025a(9) =3969a(10) =8100a(11) =16129a(12) =32761a(13) =65025a(14) =131044a(15) =261121a(16) =524176a(17) =1046529a(18) =2096704a(19) =4190209a(20) =8386816a(21) =16769025a(22) =33547264a(23) =67092481a(24) =134212225a(25) =268402689a(26) =536848900a(27) =1073676289a(28) =2147395600a(29) =4294836225