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 A160764 #6 Dec 24 2015 02:50:23
%S A160764 -1,-1,-2,-2,-2,-3,-2,-2,-2,-2,-3,-3,-2,-2,-3,-3,-2,-1,-1,-2,-2,-2,-3,
%T A160764 -2,-3,-4,-3,-4,-5,-3,-4,-2,-1,-1,-1,-1,-2,-2,-2,-1,-1,-2,-2,-2,-3,-3,
%U A160764 -3,-2,-3,-3,-2,-3,-2,-3,-3,-3,-3,-2,-3,-4,-3,-1,-2,-2,-2,-3,-3,-3,-4
%N A160764 a(n) = n-th squarefree number minus round(n*zeta(2)).
%C A160764 Race between the n-th squarefree number and round(n*zeta(2)).
%H A160764 Daniel Forgues, <a href="/A160764/b160764.txt">Table of n, a(n) for n=1..60794</a>
%F A160764 Since zeta(2) = Sum_{i>=1}, 1/(i^2) = (Pi^2)/6, we get:
%F A160764 a(n) = A005117(n) - n * Sum_{i>=1}, 1/(i^2) = O(sqrt(n));
%F A160764 a(n) = A005117(n) - n * (Pi^2)/6 = O(sqrt(n)).
%Y A160764 Cf. A005117 Squarefree numbers.
%Y A160764 Cf. A013929 Nonsquarefree numbers.
%Y A160764 Cf. A013928 Number of squarefree numbers < n.
%Y A160764 Cf. A158819 Number of squarefree numbers <= n minus round(n/zeta(2)).
%K A160764 sign
%O A160764 1,3
%A A160764 _Daniel Forgues_, May 26 2009