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 A121644 #11 Sep 04 2015 03:28:09
%S A121644 1,2,3,4,5,6,8,9,13,14,17,19,21,23,25,27,29,31,33,36,39,41,43,44,45,
%T A121644 48,49,50,52,53,59,61,63,64,65,67,68,69,72,73,75,77,82,84,86,87,88,89,
%U A121644 91,92,93,94,96,98,99,100,101,102,104,106,108,110,116,117,119,120,121,123
%N A121644 Slowest increasing sequence with squarefree cumulative sums.
%H A121644 Zak Seidov, <a href="/A121644/b121644.txt">Table of n, a(n) for n = 1..1000.</a>
%t A121644 a = {1}; Do[k = 1; While[Nand[k > a[[n]], SquareFreeQ[Sum[a[[i]], {i, n}] + k]], k++]; AppendTo[a, k], {n, 67}]; a (* _Michael De Vlieger_, Sep 03 2015 *)
%Y A121644 Cf. A084693 (non-monotonic version).
%K A121644 nonn
%O A121644 1,2
%A A121644 _Zak Seidov_, Aug 13 2006