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 A262400 #32 Dec 04 2015 23:51:03
%S A262400 0,0,0,0,-4,5,0,0,-12,9,5,0,-28,39,0,-10,-60,102,-45,0,-119,252,-132,
%T A262400 0,-252,580,-403,9,-424,1363,-1210,248,-828,3003,-3332,1195,-1729,
%U A262400 6697,-8740,4290,-3807,14514,-22176,13889,-9288,31049,-54142,41501,-25260,66885,-129570
%N A262400 Let f(x) = 1 + Sum_{j>=4} (|mu(j)| - |mu(j-1)|)*x^j, where mu(n) is the Möbius function (A008683). Then a(n) is n times the coefficient of x^n in the expansion of log(f(x)).
%C A262400 Function f(x) is connected with the density h of the exponentially squarefree numbers (A209061). Specifically, for h = Product_{prime p} f(1/p), this sequence allows the calculation of h with very high accuracy (cf. A262276).
%H A262400 Juan Arias-de-Reyna, <a href="/A262400/b262400.txt">Table of n, a(n) for n = 0..3000</a>
%t A262400 M = 50; (* to get the first 51 terms *)
%t A262400 f = 1 + Sum[(MoebiusMu[n]^2 - MoebiusMu[n - 1]^2) x^n, {n, 4, M}];
%t A262400 S = Series[Log[f], {x, 0, M}];
%t A262400 A262400[nn_] := CoefficientList[S, x][[nn + 1]] nn;
%t A262400 Table[A262400[n], {n, 0, M}]
%Y A262400 Cf. A008683, A209061, A262276.
%K A262400 sign
%O A262400 0,5
%A A262400 _Juan Arias-de-Reyna_, Sep 21 2015