Numbers k such that k and k^2 use only the digits 0, 1, 2, 4 and 7.

Terms

a(0) =0a(1) =1a(2) =2a(3) =10a(4) =11a(5) =12a(6) =20a(7) =21a(8) =100a(9) =101a(10) =102a(11) =110a(12) =120a(13) =200a(14) =201a(15) =210a(16) =421a(17) =1000a(18) =1001a(19) =1002a(20) =1010a(21) =1011a(22) =1012a(23) =1020a(24) =1021a(25) =1071a(26) =1100a(27) =1101a(28) =1102a(29) =1200