Numbers k such that k and k^2 use only the digits 1, 4, 7, 8 and 9.

Terms

a(0) =1a(1) =7a(2) =9a(3) =88a(4) =141a(5) =441a(6) =1191a(7) =4141a(8) =4471a(9) =8878a(10) =8941a(11) =9191a(12) =84779a(13) =87988a(14) =94191a(15) =97441a(16) =99471a(17) =118817a(18) =414417a(19) =847891a(20) =974417a(21) =989891a(22) =994479a(23) =4179891a(24) =4181488a(25) =4181971a(26) =9171417a(27) =9187917a(28) =9191191a(29) =9478817