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 A170830 #9 Feb 26 2019 09:30:41
%S A170830 949,1036,2362,2812,2847,3108,7086,8436,8541,9324,21258,25308,25623,
%T A170830 27972,28009,63774,63973,66124,75924,76869,83916,84027,84253,191322,
%U A170830 191919,198372,227772,230607,235228,251748,252081,252759,253216,573966,575757
%N A170830 A121153 \ A005836.
%C A170830 If n is in this sequence then so is 3n. - _Charlie Neder_, Feb 25 2019
%H A170830 Charlie Neder, <a href="/A170830/b170830.txt">Table of n, a(n) for n = 1..49</a>
%o A170830 (PARI) is1(n, R=divrem(3^logint(n, 3), n), S=0)={while(R[1]!=1&&!bittest(S, R[2]), S+=1<<R[2]; R=divrem(R[2]*3, n)); R[1]!=1||R[2]==0}
%o A170830 is2(n)={while(n, if(n%3>1, return(0)); n\=3); 1;}
%o A170830 for(n = 1, 1000000, if(is1(n), if(is2(n),,print(n)))) \\ _Charlie Neder_, Feb 26 2019, from programs for A121153 and A005836
%Y A170830 Cf. A170853, A005836, and the Cantor set sequence A121153.
%K A170830 nonn
%O A170830 1,1
%A A170830 _N. J. A. Sloane_, Feb 22 2010
%E A170830 Data corrected by _Charlie Neder_, Feb 25 2019