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 A080820 #15 Jun 08 2019 17:58:55
%S A080820 1,2,3,4,4,5,6,6,7,8,9,9,10,11,11,12,13,14,14,15,16,16,17,18,19,19,20,
%T A080820 21,21,22,23,23,24,25,26,26,27,28,28,29,30,31,31,32,33,33,34,35,35,36,
%U A080820 37,38,38,39,40,40,41,42,43,43,44,45,45,46,47,48,48,49,50,50,51,52,52
%N A080820 Least m such that m^2 >= n*(n+1)/2.
%H A080820 Harvey P. Dale, <a href="/A080820/b080820.txt">Table of n, a(n) for n = 1..1000</a>
%F A080820 a(n) = A080819(n)^(1/2).
%F A080820 a(n) = ceiling(sqrt(n*(n+1)/2)) - C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 19 2004
%p A080820 seq(ceil(sqrt(n*(n+1)/2)),n=1..80); # C. Ronaldo
%t A080820 lst = {}; m = 1; Do[While[n*(n + 1)/2 > m^2, m++]; AppendTo[lst, m], {n, 69}]; lst (* _Arkadiusz Wesolowski_, Jul 18 2012 *)
%t A080820 Ceiling[Sqrt[#]]&/@Accumulate[Range[80]] (* _Harvey P. Dale_, Feb 10 2016 *)
%Y A080820 Cf. A080817, A080818, A080819.
%K A080820 easy,nonn
%O A080820 1,2
%A A080820 _Amarnath Murthy_, Mar 21 2003
%E A080820 More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 19 2004
%E A080820 Name changed by _Arkadiusz Wesolowski_, Jul 18 2012