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 A081783 #18 Apr 24 2025 01:30:19
%S A081783 1,4,172,181307,241328833528,824652019956267685427678,
%T A081783 768422457901766762303892554138930904416139509281,
%U A081783 2110688056630901907060877896737932376507936264268382076456539236145849709148481095915090382331184
%N A081783 Continued cotangent for zeta(2) = Pi^2/6.
%F A081783 Pi^2/6 = cot(Sum_{n>=0} (-1)^n*acot(a(n))).
%F A081783 Let b(0) = Pi^2/6, b(n) = (b(n-1)*floor(b(n-1))+1)/(b(n-1)-floor(b(n-1))) then a(n) = floor(b(n)).
%o A081783 (PARI) \p900
%o A081783 bn=vector(100);
%o A081783 bn[1]=Pi^2/6;
%o A081783 b(n)=if(n<0,0,bn[n]);
%o A081783 for(n=2,10,bn[n]=(b(n-1)*floor(b(n-1))+1)/(b(n-1)-floor(b(n-1))));
%o A081783 a(n)=floor(b(n+1));
%Y A081783 Cf. A001620, A002666, A002667.
%K A081783 nonn
%O A081783 0,2
%A A081783 _Benoit Cloitre_, Apr 10 2003