Numbers k such that k and k^2 use only the digits 1, 2, 4, 7 and 8.

Terms

a(0) =1a(1) =2a(2) =11a(3) =12a(4) =21a(5) =22a(6) =28a(7) =88a(8) =122a(9) =221a(10) =278a(11) =418a(12) =421a(13) =471a(14) =472a(15) =478a(16) =1478a(17) =1488a(18) =2778a(19) =2878a(20) =4141a(21) =4271a(22) =4721a(23) =8472a(24) =8878a(25) =11141a(26) =14771a(27) =21171a(28) =21778a(29) =27771