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 A290971 #9 Aug 27 2017 23:13:03
%S A290971 1,2,0,6,0,-6,0,54,0,-30,0,-114,0,-126,0,4470,0,-294,0,-5850,0,-2046,
%T A290971 0,-92418,0,-8190,0,-247674,0,2010,0,30229110,0,-131070,0,-8200914,0,
%U A290971 -524286,0,-362617770,0,183162,0,-354416634,0,-8388606,0,-53614489794,0
%N A290971 Write x/(1-x) in the form Sum_{j>=1} a(j)*x^j/(1+a(j)*x^j).
%F A290971 a(n) = -Sum_t (-1)^v(t) where the sum is over all same-trees of weight n (see A281145 for definition) and v(t) is the number of nodes (branchings and leaves) in t.
%t A290971 nn=20;-Solve[Table[Sum[a[n/d]^d,{d,Divisors[n]}]==-1,{n,nn}],Array[a,nn]][[1,All,2]]
%Y A290971 Cf. A048272, A220418, A260685, A273873, A275870, A281145, A289078, A289501, A290261, A290973.
%K A290971 sign
%O A290971 1,2
%A A290971 _Gus Wiseman_, Aug 16 2017