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 A118026 #12 Sep 16 2017 20:15:03
%S A118026 0,1,3,5,9,13,19,26,34,42,52,63,75,87,101,116,132,149,167,185,205,226,
%T A118026 248,271,295,320,345,372,400,429,459,490,522,555,588,623,659,696,734,
%U A118026 773,813,854,895,938,982,1027,1073,1120,1168,1217,1267,1318,1369,1422
%N A118026 a(0) = 0, a(n) = a(n-1) + (largest integer which is <= n and is missing from the earlier terms of the sequence).
%H A118026 Michael De Vlieger, <a href="/A118026/b118026.txt">Table of n, a(n) for n = 0..10000</a>
%t A118026 a = {1}; Do[AppendTo[a, a[[i - 1]] + SelectFirst[Reverse@ Range[i], FreeQ[a, #] &]], {i, 2, 53}]; {0}~Join~a (* _Michael De Vlieger_, Sep 16 2017 *)
%Y A118026 Cf. A118027, A118028, A118029, A118030, A094589.
%K A118026 easy,nonn
%O A118026 0,3
%A A118026 _Leroy Quet_, Apr 10 2006
%E A118026 More terms from Sheedeh Dorri (spd145(AT)psu.edu) and Melissa Donovan (msd181(AT)psu.edu), Apr 18 2006