Numbers k such that k and k^2 use only the digits 1, 2, 4, 7 and 9.

Terms

a(0) =1a(1) =2a(2) =7a(3) =11a(4) =12a(5) =21a(6) =27a(7) =171a(8) =212a(9) =421a(10) =479a(11) =2729a(12) =2777a(13) =4911a(14) =4912a(15) =11171a(16) =21729a(17) =44127a(18) =49777a(19) =112912a(20) =119127a(21) =221911a(22) =279271a(23) =471479a(24) =477412a(25) =492921a(26) =497212a(27) =499479a(28) =974229a(29) =1194771