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 A137019 Numbers k such that k and k^2 use only the digits 1, 2, 7 and 9. 0

%I

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

%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

%O 1,2

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

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Last modified November 28 12:45 EST 2021. Contains 349403 sequences. (Running on oeis4.)