Numbers k such that k and k^2 use only the digits 0, 2, 4, 7 and 9.

Terms

a(0) =0a(1) =2a(2) =7a(3) =20a(4) =27a(5) =47a(6) =70a(7) =97a(8) =200a(9) =270a(10) =470a(11) =497a(12) =700a(13) =970a(14) =997a(15) =2000a(16) =2700a(17) =4700a(18) =4970a(19) =4997a(20) =7000a(21) =9700a(22) =9970a(23) =9997a(24) =20000a(25) =22247a(26) =27000a(27) =44747a(28) =44777a(29) =47000