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 A153818 #19 May 26 2021 12:01:15
%S A153818 1,5,12,22,35,53,72,96,123,153,184,222,260,304,351,402,453,510,568,
%T A153818 633,697,765,839,916,994,1077,1164,1252,1342,1443,1535,1641,1747,1856,
%U A153818 1969,2083,2200,2321,2447,2579,2705,2844,2979,3123,3269,3417,3570,3726,3881
%N A153818 a(n) = Sum_{k=1..n} floor(n^2/k^2).
%C A153818 How can Sum_{k=1..n} floor(n^2/k^2) be expressed as a function of Sum_{k=1..n} floor(n/k)? [_Ctibor O. Zizka_, Feb 14 2009]
%H A153818 Seiichi Manyama, <a href="/A153818/b153818.txt">Table of n, a(n) for n = 1..10000</a>
%H A153818 Benoit Cloitre, <a href="/A153818/a153818.png">Plot of (a(n)-zeta(2)*n^2-zeta(1/2)*n)/(n^0.5/log(n))</a>
%F A153818 From _Benoit Cloitre_, Jan 22 2013: (Start)
%F A153818 Asymptotic formula: a(n) = zeta(2)*n^2 + zeta(1/2)*n + O(n^(1/2)).
%F A153818 Conjecture: a(n) = zeta(2)*n^2 + zeta(1/2)*n + O(n^0.5/log(n)) (see link). (End)
%e A153818 a(4)=22 because floor(16/1) + floor(16/4) + floor(16/9) + floor(16,16) = 16 + 4 + 1 + 1 = 22. [_Emeric Deutsch_, Jan 13 2009]
%p A153818 a := proc (n) options operator, arrow: sum(floor(n^2/k^2), k = 1 .. n) end proc: seq(a(n), n = 1 .. 50); # _Emeric Deutsch_, Jan 13 2009
%o A153818 (PARI) a(n)=sum(k=1,n,n^2\k^2) \\ _Benoit Cloitre_, Jan 22 2013
%Y A153818 Cf. A006218, A344675.
%K A153818 easy,nonn
%O A153818 1,2
%A A153818 _Ctibor O. Zizka_, Jan 02 2009
%E A153818 Definition edited by _Emeric Deutsch_, Jan 13 2009
%E A153818 Extended by _Emeric Deutsch_, Jan 13 2009