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 A170920 #9 Oct 04 2019 22:19:03
%S A170920 -1,-1,-1,-16,-91,-58844,-73267,-1196588,-49830764,-1715330699,
%T A170920 -35249288479,-374085503198546,-732125336837021,-779432268293710651,
%U A170920 -30015706187367326893,-183998031852529374082,-46789354983174555461,-115977125342651266593554,-248130101882943187003954597,-13171311382437535379302071714878
%N A170920 Write x*cot(x) = Product_{n>=1} (1 + g_n*x^(2*n)); a(n) = numerator(g_n).
%e A170920 -1/3, -1/45, -1/105, -16/4725, -91/66825, -58844/127702575, -73267/383107725, ...
%p A170920 t1:=x*cot(x);
%p A170920 L:=100;
%p A170920 t0:=series(t1, x, L);
%p A170920 g:=[];
%p A170920 M:=20; # number of terms to get
%p A170920 t2:=t0:
%p A170920 for n from 1 to M do
%p A170920 t3:=coeff(t2, x, 2*n); t2:=series(t2/(1+t3*x^(2*n)), x, L); g:=[op(g), t3];
%p A170920 od:
%p A170920 g;
%p A170920 g1:=map(numer, g);
%p A170920 g2:=map(denom, g);
%Y A170920 Cf. A170921, A170908-A170919.
%K A170920 sign,frac
%O A170920 1,4
%A A170920 _N. J. A. Sloane_, Jan 31 2010
%E A170920 Corrected definition and terms - _N. J. A. Sloane_, Oct 04 2019 (thanks to _Petros Hadjicostas_ for pointing out that something was wrong).