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 A144429 #6 Jul 31 2015 21:40:13
%S A144429 1,2,3,4,6,9,10,12,15,16,18,21,22,24,27,28,30,33,34,36,39,40,42,45,46,
%T A144429 48,51,52,54,57,58,60,63,64,66,69,70,72,75,76,78,81,82,84,87,88,90,93,
%U A144429 94,96,99,100,102,105,106,108,111,112,114,117,118,120,123,124,126,129
%N A144429 Starts 1 2 3 then successive terms have differences 1 2 3.
%C A144429 Essentially the same sequence as A047231. - Stefan Steinerberger, Oct 17 2008
%H A144429 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 1, -1).
%F A144429 G.f.: x(1+x)(1+x^2-x^3+2x^4)/((1+x+x^2)(1-x)^2). a(n)=a(n-3)+6, n>5. a(n) = 2n -11/3 +A099837(n+3)/3, n>2. [From _R. J. Mathar_, Oct 15 2008]
%t A144429 Join[{1,2},LinearRecurrence[{1,0,1,-1},{3,4,6,9},100]] (* or *) nxt[ {a_,b_,c_}]:= {c+1,c+3,c+6}; Flatten[NestList[nxt,{1,2,3},30]] (* _Harvey P. Dale_, Nov 23 2012 *)
%Y A144429 Cf. A144430, A047231.
%K A144429 nonn,easy
%O A144429 1,2
%A A144429 Milton L. Brown (miltbrown(AT)earthlink.net), Oct 13 2008
%E A144429 Extended by _R. J. Mathar_, Oct 15 2008