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%I #13 Oct 14 2019 04:27:12
%S 7,11,13,19,20,23,27,28,29,30,33,34,35,36,37,38,39,42,43,48,50,51,54,
%T 55,57,58,60,61,63,68,69,74,79,80,87,88,90,91,93,94,113,115,121,128,
%U 130,139,149,150,168,169,172,173,174,187,229,337,338,376,417
%N Numbers k such that 2^k contains 2^3=8 as its largest proper substring of the form 2^m (probably finite).
%t sub2[n_] := Block[{s = ToString[2^n], k = n - 1}, While[k >= 0 && ! StringContainsQ[s, ToString[2^k]], k--]; k]; Select[Range[500], sub2[#] == 3 &] (* _Giovanni Resta_, Oct 14 2019 *)
%Y Cf. A033921.
%K nonn,base
%O 1,1
%A _Patrick De Geest_, Jun 15 1998
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