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Numbers k such that k and k^2 use only the digits 1, 5, 6, 7 and 8.
1

%I #9 Apr 12 2024 09:51:27

%S 1,76,81,766,816,881,7181,7666,71881,76666,81681,81766,88181,88776,

%T 766666,767181,817666,817776,876766,7666666,7866881,8115766,8176666,

%U 76666666,81766666,81767181,87617166,87857166,88157181,88761881,766587576,766658716,766658776,766666666,767187576,785187166,811657666,811711881,816156766

%N Numbers k such that k and k^2 use only the digits 1, 5, 6, 7 and 8.

%C Generated with DrScheme.

%H Jonathan Wellons, <a href="/A137060/b137060.txt">Table of n, a(n) for n = 1..187</a>

%H J. Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]

%e 876861765716681^2 = 768886556175775558717561655761.

%t With[{c={1,5,6,7,8}},Select[Flatten[Table[FromDigits/@Tuples[c,n],{n,9}]], SubsetQ[c,IntegerDigits[#^2]]&]] (* _Harvey P. Dale_, Nov 15 2018 *)

%K base,nonn

%O 1,2

%A Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008