Nonsquares mod 27.

Terms

a(0) =2a(1) =3a(2) =5a(3) =6a(4) =8a(5) =11a(6) =12a(7) =14a(8) =15a(9) =17a(10) =18a(11) =20a(12) =21a(13) =23a(14) =24a(15) =26