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 A118028 #12 Sep 19 2017 21:37:32
%S A118028 1,3,5,9,13,19,25,32,40,50,60,71,83,97,111,126,142,159,177,197,217,
%T A118028 238,260,283,307,333,359,386,414,443,473,504,537,570,604,639,675,712,
%U A118028 750,789,830,871,913,956,1000,1045,1091,1138,1186,1235,1286,1337,1389,1442
%N A118028 a(0)=1. a(n) = a(n-1) + (smallest integer which is >= n and is missing from the earlier terms of the sequence).
%H A118028 Michael De Vlieger, <a href="/A118028/b118028.txt">Table of n, a(n) for n = 0..1000</a>
%t A118028 a = {1}; Do[k = 2; While[Nand[FreeQ[a, k], k >= i], k++]; AppendTo[a, a[[i]] + k], {i, 53}]; a (* _Michael De Vlieger_, Sep 19 2017 *)
%Y A118028 Cf. A118026, A118027, A118029, A118030, A094589.
%K A118028 easy,nonn
%O A118028 0,2
%A A118028 _Leroy Quet_, Apr 10 2006
%E A118028 More terms from _Joshua Zucker_, Jul 27 2006