When squared gives number composed of digits {1,4,6}.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =12a(5) =21a(6) =38a(7) =108a(8) =119a(9) =121a(10) =129a(11) =204a(12) =408a(13) =804a(14) =2538a(15) =3408a(16) =6642a(17) =12908a(18) =25771a(19) =78196a(20) =81619a(21) =333858a(22) =204000408a(23) =668164962a(24) =813118358a(25) =4018285038a(26) =12006850738a(27) =12694138988a(28) =12706943631a(29) =40182224262