Squares that remain squares when prefixed with a 6.

Terms

a(0) =4a(1) =25a(2) =400a(3) =2500a(4) =40000a(5) =250000a(6) =2805625a(7) =4000000a(8) =25000000a(9) =36300625a(10) =43890625a(11) =221265625a(12) =280562500a(13) =400000000a(14) =2500000000a(15) =3630062500a(16) =4389062500a(17) =22126562500a(18) =28056250000a(19) =40000000000a(20) =250000000000a(21) =363006250000a(22) =438906250000