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 A080646 #14 Feb 25 2015 23:32:50
%S A080646 3,4,8,12,13,14,15,16,17,18,19,20,24,28,32,36,40,44,48,52,53,54,55,56,
%T A080646 57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,
%U A080646 80,81,82,83,84,88,92,96,100,104,108,112,116,120,124,128,132,136,140,144,148,152,156,160,164,168
%N A080646 a(1) = 3; for n>1, a(n) is taken to be the smallest integer greater than a(n-1) which is consistent with the condition "if n is a member of the sequence then a(n) is divisible by 3".
%H A080646 B. Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL6/Cloitre/cloitre2.html">Numerical analogues of Aronson's sequence</a>, J. Integer Seqs., Vol. 6 (2003), #03.2.2.
%H A080646 B. Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="http://arXiv.org/abs/math.NT/0305308">Numerical analogues of Aronson's sequence</a> (math.NT/0305308)
%H A080646 <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>
%F A080646 For k>=2 and i=0, ..., 4^k/2, a((4/3)*(4^(k-1)-1) + i) = (5*4^k-8)/6 + i, a((5*4^k-8)/6 + i) = (4/3)*(4^k-1) + 4*i. - _N. J. A. Sloane_, Mar 02 2003
%F A080646 {a(a(n))} = {4i, i >= 2}.
%Y A080646 Cf. A080639, A080640, A079000.
%K A080646 nonn,easy
%O A080646 1,1
%A A080646 _Benoit Cloitre_, Feb 12 2003