Numbers k such that k and k^2 use only the digits 1, 2, 5 and 6.

Terms

a(0) =1a(1) =5a(2) =11a(3) =15a(4) =16a(5) =25a(6) =125a(7) =511a(8) =515a(9) =516a(10) =1125a(11) =2261a(12) =5125a(13) =12511a(14) =12515a(15) =25525a(16) =51211a(17) =125125a(18) =5162515a(19) =51626211a(20) =125162515a(21) =5162525125