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 A118027 #12 Sep 16 2017 19:57:28
%S A118027 0,1,3,7,11,16,22,30,38,47,57,69,81,94,108,123,140,157,175,194,214,
%T A118027 235,258,281,305,330,356,383,411,440,471,502,534,567,601,636,672,709,
%U A118027 748,787,827,868,910,953,997,1042,1088,1136,1184,1233,1283,1334,1386,1439
%N A118027 a(0) = 0, a(n) = a(n-1) + (smallest integer which is >= n and is missing from the earlier terms of the sequence).
%H A118027 Michael De Vlieger, <a href="/A118027/b118027.txt">Table of n, a(n) for n = 0..10000</a>
%t A118027 a = {1}; Do[k = i; While[MemberQ[a, k], k++]; AppendTo[a, a[[i - 1]] + k], {i, 2, 53}]; {0}~Join~a (* _Michael De Vlieger_, Sep 16 2017 *)
%Y A118027 Cf. A118026, A118028, A118029, A118030, A094589.
%K A118027 easy,nonn
%O A118027 0,3
%A A118027 _Leroy Quet_, Apr 10 2006
%E A118027 More terms from Wendy Kalasky (wkk107(AT)psu.edu), Apr 26 2006