Numbers k such that k and k^2 use only the digits 1, 2, 4, 5 and 7.

Terms

a(0) =1a(1) =2a(2) =5a(3) =11a(4) =12a(5) =15a(6) =21a(7) =112a(8) =211a(9) =415a(10) =421a(11) =521a(12) =715a(13) =2271a(14) =5211a(15) =21271a(16) =21715a(17) =27412a(18) =75771a(19) =125521a(20) =145415a(21) =724412a(22) =742412a(23) =1127715a(24) =1214171a(25) =1475515a(26) =2115211a(27) =2125421a(28) =2127715a(29) =2171271