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 A216545 #22 Feb 04 2025 10:10:43
%S A216545 1,5,7,0,7,9,5,3,2,6,7,9,4,8,9,6,6,2,0,2,3,1,3,2,1,6,9,1,6,3,4,7,5,1,
%T A216545 4,4,2,0,9,8,6,4,5,6,9,9,6,8,7,5,5,1,5,2,5,4,8,7,4,7,2,3,4,6,6,7,4,9,
%U A216545 0,8,2,0,0,4,4,0,3,3,9,4,9,9,5,1,3,3,7,8,3,9,3,6,5,1,6,6,7,0,2,1,8,4,8,4,7,8,9,2,2,9,3,1,7,1,1,7,8,2,1,3,5,3,7,8,7
%N A216545 Decimal expansion of 2*Sum_{k=1..500000} (-1)^(k-1)/(2k-1).
%C A216545 An approximation to Pi/2. The constant is rational, by definition (a product of finitely many rational numbers).
%H A216545 J. M. Borwein, P. B. Borwein and K. Dilcher, <a href="http://www.jstor.org/stable/2324715">Pi, Euler numbers and asymptotic expansions</a>, Amer. Math. Monthly, 96 (1989), 681-687.
%H A216545 J. M. Borwein and R. M. Corless, <a href="http://www.cecm.sfu.ca/~jborwein/sloane/sloane.html">Review of "An Encyclopedia of Integer Sequences" by N. J. A. Sloane and Simon Plouffe</a>, SIAM Review, 38 (1996), 333-337.
%H A216545 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>.
%e A216545 1.57079532679489662023132169163475144209864569968755152548747...
%Y A216545 Cf. A000796, A216542, A013706, A216543, A216544, A216545, A013705, A216546, A216547, A216548.
%Y A216545 Cf. also A013707, A195793.
%K A216545 cons,nonn,easy
%O A216545 1,2
%A A216545 _N. J. A. Sloane_, Sep 08 2012