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%I #11 Apr 12 2024 09:51:27
%S 1,881,88776,7866881
%N Numbers k such that k and k^2 use only the digits 1, 6, 7 and 8.
%C Generated with DrScheme.
%C No additional terms through 10^10. - _Harvey P. Dale_, Apr 26 2015
%C No additional terms through 10^27. - _Robert Israel_, Nov 23 2023
%H J. Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]
%e 7866881^2 = 61887816668161.
%p Good:= {1,6,7,8}:
%p G[1]:= {1,6}: R:= 1;
%p for d from 2 to 27 do
%p G[d]:= select(t -> member(floor((t^2 mod 10^d)/10^(d-1)),Good), map(t -> seq(10^(d-1)*i+t, i=Good), G[d-1]));
%p for t in G[d] do
%p if convert(convert(t^2,base,10),set) subset Good then R:= R,t fi
%p od
%p od:
%p sort([R]); # _Robert Israel_, Nov 23 2023
%t With[{c={1,6,7,8}},Select[Flatten[Table[FromDigits/@Tuples[c,n],{n,7}]],SubsetQ[c,IntegerDigits[#^2]]&]] (* _Harvey P. Dale_, Apr 26 2015 *)
%K base,nonn,changed
%O 1,2
%A Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008
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