Numbers k such that k and k^2 use only the digits 2, 4, 5, 7 and 8.

Terms

a(0) =2a(1) =5a(2) =22a(3) =28a(4) =85a(5) =88a(6) =278a(7) =472a(8) =478a(9) =522a(10) =528a(11) =888a(12) =2878a(13) =5278a(14) =7588a(15) =27485a(16) =47485a(17) =74528a(18) =87878a(19) =242585a(20) =275472a(21) =522282a(22) =745485a(23) =885582a(24) =2782485a(25) =2784878a(26) =2878278a(27) =8845778a(28) =8874528a(29) =24257485