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

Terms

a(0) =0a(1) =7a(2) =70a(3) =97a(4) =700a(5) =970a(6) =997a(7) =7000a(8) =9700a(9) =9970a(10) =9997a(11) =70000a(12) =97000a(13) =99700a(14) =99970a(15) =99997a(16) =700000a(17) =970000a(18) =997000a(19) =999700a(20) =999970a(21) =999997a(22) =7000000a(23) =9700000a(24) =9970000a(25) =9997000a(26) =9999700a(27) =9999970a(28) =9999997a(29) =70000000