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 A190640 #28 Jul 25 2020 15:18:14
%S A190640 2,8,20,26,56,62,74,80,164,170,182,188,218,224,236,242,488,494,506,
%T A190640 512,542,548,560,566,650,656,668,674,704,710,722,728,1460,1466,1478,
%U A190640 1484,1514,1520,1532,1538,1622,1628,1640,1646,1676,1682,1694,1700,1946,1952,1964,1970,2000,2006,2018,2024,2108,2114,2126
%N A190640 Numbers whose base-3 expansion ends in 2 and does not contain any 1's.
%H A190640 Vincenzo Librandi, <a href="/A190640/b190640.txt">Table of n, a(n) for n = 1..1000</a>
%F A190640 Conjecture: a(n) = A055246(n) + 1. - _Michel Marcus_, Aug 24 2016
%F A190640 a(n) = A005823(2n). - _Charles R Greathouse IV_, Aug 24 2016
%t A190640 Select[Range[2200],Last[IntegerDigits[#,3]]==2&&DigitCount[#,3,1]==0&] (* _Harvey P. Dale_, Sep 09 2012 *)
%t A190640 FromDigits[#,3]&/@(Join[#,{2}]&/@Tuples[{0,2},7]) (* _Harvey P. Dale_, Jul 25 2020 *)
%o A190640 (PARI) is(n)=n%3==2 && setsearch(Set(digits(n,3)), 1)==0 \\ _Charles R Greathouse IV_, Aug 24 2016
%o A190640 (PARI) a(n)=2*fromdigits(binary(2*n-1),3) \\ _Charles R Greathouse IV_, Aug 24 2016
%Y A190640 Subsequence of A005823.
%Y A190640 Cf. A005836.
%K A190640 nonn,base,easy
%O A190640 1,1
%A A190640 _N. J. A. Sloane_, May 15 2011