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 A074939 #34 Jun 26 2025 18:08:31
%S A074939 0,4,10,12,28,30,36,40,82,84,90,94,108,112,118,120,244,246,252,256,
%T A074939 270,274,280,282,324,328,334,336,352,354,360,364,730,732,738,742,756,
%U A074939 760,766,768,810,814,820,822,838,840,846,850,972,976,982,984,1000,1002
%N A074939 Even numbers such that base 3 representation contains no 2.
%C A074939 Even numbers in A005836; n such that binomial(2n,n) == 1 (mod 3).
%C A074939 Sum of an even number of distinct powers of 3. - _Emeric Deutsch_, Dec 03 2003
%H A074939 Amiram Eldar, <a href="/A074939/b074939.txt">Table of n, a(n) for n = 0..10000</a>
%H A074939 Emeric Deutsch and B. E. Sagan, <a href="https://arxiv.org/abs/math/0407326">Congruences for Catalan and Motzkin numbers and related sequences</a>, arXiv:math/0407326 [math.CO], 2004.
%H A074939 Emeric Deutsch and B. E. Sagan, <a href="https://doi.org/10.1016/j.jnt.2005.06.005">Congruences for Catalan and Motzkin numbers and related sequences</a>, J. Num. Theory 117 (2006), 191-215.
%F A074939 a(n) = A083094(n)/2; a(n) mod 3 = A010060(n); n such that coefficient of x^n equals 1 in Product_{k>=0} (1 - x^(3^k)).
%F A074939 a(n) + A074938(n) = A055246(n+1). - _Philippe Deléham_, Jul 10 2005
%t A074939 Select[2*Range[0,600],DigitCount[#,3,2]==0&] (* _Harvey P. Dale_, Dec 10 2016 *)
%o A074939 (Python)
%o A074939 def A074939(n): return int(bin((n.bit_count()&1)+(n<<1))[2:],3) # _Chai Wah Wu_, Jun 26 2025
%Y A074939 Intersection of A005843 and A005836.
%Y A074939 Cf. A006996, A010060, A055246, A074938, A083095.
%K A074939 easy,nonn
%O A074939 0,2
%A A074939 _Benoit Cloitre_, Oct 04 2002; Nov 15 2003