Numbers k such that k and k^2 use only the digits 1, 2, 5, 7 and 8.

Terms

a(0) =1a(1) =5a(2) =11a(3) =15a(4) =85a(5) =285a(6) =715a(7) =1585a(8) =2285a(9) =8711a(10) =28511a(11) =52515a(12) =52715a(13) =72285a(14) =151285a(15) =228511a(16) =285515a(17) =722211a(18) =852715a(19) =878511a(20) =2858711a(21) =2878511a(22) =7182285a(23) =7182515a(24) =7271285a(25) =8785711a(26) =8877811a(27) =8881585a(28) =15878511a(29) =28551285