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 A216547 #25 Feb 04 2025 10:10:51
%S A216547 1,5,7,0,7,9,6,2,2,6,7,9,4,8,9,6,6,1,9,2,3,2,3,2,1,6,9,1,6,3,9,7,5,1,
%T A216547 3,9,2,0,9,8,5,8,4,6,9,9,6,9,3,6,5,2,9,1,0,4,8,7,4,7,0,9,1,1,1,5,3,9,
%U A216547 0,8,2,0,3,6,4,8,3,1,4,4,9,9,3,1,3,7,4,7,1,3,6,1,7,1,0,5,8,7,3,3,3,5,2,0,5,5,0,4,3,0,6,2,7,2,6,0,3,1,8,7,3,7,8,7,4
%N A216547 Decimal expansion of 2*Sum_{k=1..5000000} (-1)^(k-1)/(2k-1).
%C A216547 An approximation to Pi/2. The constant is rational, by definition (a product of finitely many rational numbers).
%H A216547 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 A216547 J. M. Borwein, P. B. Borwein and K. Dilcher, <a href="https://doi.org/10.1007/978-3-319-32377-0_12">Pi, Euler numbers and asymptotic expansions</a>, in Pi: The Next Generation (2016) pp. 197-205.
%H A216547 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 A216547 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>.
%e A216547 1.57079622679489661923232169163975139209858469969365291048747...
%Y A216547 Cf. A000796, A216542, A013706, A216543, A216544, A216545, A013705, A216546, A216547, A216548.
%Y A216547 Cf. also A013707, A195793.
%K A216547 cons,nonn,easy
%O A216547 1,2
%A A216547 _N. J. A. Sloane_, Sep 08 2012