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 A077599 #11 Aug 09 2015 14:26:13
%S A077599 8,9,24,45,100,117,120,125,135,171,175,180,184,224,243,248,256,261,
%T A077599 270,304,312,324,342,343,344,360,369,405,459,468,472,475,477,486,507,
%U A077599 513,520,531,536,578,584,603,608,625,639,640,657,664,675,704,711,720,728
%N A077599 Sequence of n such that -1 is a "double" root for M(n,x) (i.e., M(n,x)=(x+1)^2*Q(n,x)).
%C A077599 The n-th Moebius polynomial M(n,x) satisfies M(n,-1)=mu(n), the Moebius function of n; thus -1 is a simple root of M(n,x) if n is not squarefree. Hence these values could be called "double nonsquarefree numbers".
%C A077599 The n-th polynomial is divisible by (x+1)^3 for n=175, 343, 513, 800, 875. - _T. D. Noe_, Jan 09 2008
%t A077599 a[n_,1]=1; a[n_,k_]:=a[n, k]=Sum[Floor[n/m] a[m,k-1], {m,n-1}]; t={}; Do[p=Table[a[n,k], {k,n}].(x^Range[0,n-1]); If[PolynomialMod[p,(x+1)^2]==0, AppendTo[t,n]], {n,100}]; t (* _T. D. Noe_, Jan 09 2008 *)
%Y A077599 Cf. A074586, A074587, A077596, A077597, A077598, A077600, A077601.
%K A077599 nonn
%O A077599 1,1
%A A077599 _Benoit Cloitre_ and _Paul D. Hanna_, Nov 10 2002
%E A077599 More terms from _T. D. Noe_, Jan 09 2008