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A137108 Numbers k such that k and k^2 use only the digits 2, 4, 7 and 9. 0

%I #6 Jul 05 2021 10:46:12

%S 2,7,27,49777,4994777,49994777,499979277

%N Numbers k such that k and k^2 use only the digits 2, 4, 7 and 9.

%C Generated with DrScheme.

%H J. Wellons, <a href="http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a>

%e 499979277^2 = 249979277429442729.

%t okQ[n_]:=Module[{id=Union[IntegerDigits[n^2]]},And@@Table[MemberQ[ {2,4,7,9}, id[[i]]],{i,Length[id]}]]; Flatten[Table[Select[ FromDigits/@ Tuples[{2,4,7,9},d],okQ],{d,10}]] (* _Harvey P. Dale_, Jun 26 2012 *)

%K base,nonn

%O 1,1

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

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)