%I #17 May 10 2024 09:26:12
%S 1,11,27,2777
%N Numbers k such that k and k^2 use only the digits 1, 2, 7 and 9.
%C Generated with DrScheme.
%C No further terms up to 9999999999. - _Harvey P. Dale_, Oct 13 2020
%C a(5) > 10^15 if it exists. - _Chai Wah Wu_, May 25 2021
%H Jonathan Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]
%e 2777^2 = 7711729, so 2777 is a term.
%t With[{c={1,2,7,9}},Select[FromDigits/@Flatten[Table[Tuples[c,n],{n,4}],1],SubsetQ[ c,IntegerDigits[#^2]]&]] (* _Harvey P. Dale_, Oct 13 2020 *)
%o (Python)
%o from itertools import product
%o A137019_list = [n for n in (int(''.join(d)) for l in range(1,9) for d in product('1279',repeat=l)) if set(str(n**2)) <= set('1279')] # _Chai Wah Wu_, May 25 2021
%K base,nonn,more
%O 1,2
%A Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008