Squares mod 54.

Terms

a(0) =0a(1) =1a(2) =4a(3) =7a(4) =9a(5) =10a(6) =13a(7) =16a(8) =19a(9) =22a(10) =25a(11) =27a(12) =28a(13) =31a(14) =34a(15) =36a(16) =37a(17) =40a(18) =43a(19) =46a(20) =49a(21) =52