Squares and twice squares.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =9a(5) =16a(6) =18a(7) =25a(8) =32a(9) =36a(10) =49a(11) =50a(12) =64a(13) =72a(14) =81a(15) =98a(16) =100a(17) =121a(18) =128a(19) =144a(20) =162a(21) =169a(22) =196a(23) =200a(24) =225a(25) =242a(26) =256a(27) =288a(28) =289a(29) =324