This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A285803 #15 Dec 20 2021 02:36:50
%S A285803 37,87,137,187,237,287,337,357,367,370,371,372,373,374,375,376,377,
%T A285803 378,379,387,397,437,487,537,587,637,687,735,736,737,738,739,785,786,
%U A285803 787,788,789,837,857,867,870,871,872,873,874,875,876,877,878,879,887,897,937
%N A285803 Numbers k such that both k and 2k contain the digit 7.
%e A285803 37 is in the sequence because 2 * 37 = 74, which has one 7.
%e A285803 47 is not in the sequence because 2 * 47 = 94, which has no 7's.
%t A285803 Select[Range[10^3], Times @@ Boole@ Map[DigitCount[#, 10, 7] > 0 &, # {1, 2}] > 0 &] (* _Michael De Vlieger_, Apr 26 2017 *)
%Y A285803 Cf. A039938.
%K A285803 nonn,base
%O A285803 1,1
%A A285803 _J. Lowell_, Apr 26 2017