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

Terms

a(0) =0a(1) =1a(2) =10a(3) =100a(4) =1000a(5) =1071a(6) =10000a(7) =10710a(8) =100000a(9) =107100a(10) =1000000a(11) =1071000a(12) =10000000a(13) =10710000a(14) =100000000a(15) =107100000a(16) =1000000000a(17) =1071000000a(18) =10000000000a(19) =10710000000a(20) =100000000000a(21) =107100000000a(22) =1000000000000