Numbers k such that k and k^2 use only the digits 0, 4, 7, 8 and 9.

Terms

a(0) =0a(1) =7a(2) =70a(3) =88a(4) =97a(5) =700a(6) =707a(7) =878a(8) =880a(9) =948a(10) =970a(11) =997a(12) =7000a(13) =7007a(14) =7070a(15) =8780a(16) =8798a(17) =8800a(18) =8947a(19) =9480a(20) =9700a(21) =9898a(22) =9970a(23) =9997a(24) =70000a(25) =70007a(26) =70070a(27) =70700a(28) =70707a(29) =87798