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 A309286 #12 Jul 22 2019 12:00:20
%S A309286 0,1,0,0,1,1,1,1,0,-1,-1,-1,-1,-1,-1,-1,1,1,2,2,2,2,2,2,2,1,1,1,1,1,1,
%T A309286 1,-1,-1,-1,-1,-2,-2,-2,-2,-2,-2,-2,-2,-2,-2,-2,-2,-2,-3,-2,-2,-2,-2,
%U A309286 -2,-2,-2,-2,-2,-2,-2,-2,-2,-2,2,2,2,2,2,2,2,2,3,3
%N A309286 a(0) = 0, a(1) = 1, and for any n > 1, a(n) = Sum_{k > 1} (-1)^k * a(floor(n/k^2)).
%C A309286 This sequence is a signed variant of A309262.
%H A309286 Rémy Sigrist, <a href="/A309286/b309286.txt">Table of n, a(n) for n = 0..10000</a>
%e A309286 a(9) = a(floor(9/2^2)) - a(floor(9/3^3)) = a(2) - a(1) = 0 - 1 = -1.
%t A309286 Join[{0}, Clear[a]; a[0]=0; a[1]=1; a[n_]:=a[n]=Sum[a[Floor[n/k^2]](-1)^k, {k, 2, n}]; Table[a[n], {n, 1, 100}]] (* _Vincenzo Librandi_, Jul 22 2019 *)
%o A309286 (PARI) a(n) = if (n<=1, n, sum (k=2, sqrtint(n), (-1)^k * a(n\k^2)))
%Y A309286 Cf. A309262.
%K A309286 sign
%O A309286 0,19
%A A309286 _Rémy Sigrist_, Jul 21 2019