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A216543 Decimal expansion of 4*Sum_{k=1..50000} (-1)^(k-1)/(2k-1).

%I A216543 #25 Feb 04 2025 10:03:49
%S A216543 3,1,4,1,5,7,2,6,5,3,5,8,9,7,9,5,2,3,8,4,6,2,6,4,2,3,8,3,2,7,9,5,0,4,
%T A216543 1,0,4,1,9,7,1,6,6,6,2,9,3,7,5,1,1,5,9,2,5,1,7,4,8,9,0,5,3,7,0,0,8,2,
%U A216543 1,5,1,2,8,2,4,4,3,3,0,6,9,6,2,4,7,1,3,2,4,1,8,1,1,0,1,9,4,7,0,5,3,7,6,8,7,2,6,5,4,8,5,0,1,8,7,4,0,9,6,5,0,1,2,3,8
%N A216543 Decimal expansion of 4*Sum_{k=1..50000} (-1)^(k-1)/(2k-1).
%C A216543 An approximation to Pi. The constant is rational, by definition (a product of finitely many rational numbers).
%H A216543 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 A216543 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 A216543 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>.
%e A216543 3.14157265358979523846264238327950410419716662937511592517489...
%t A216543 First[RealDigits[4*Sum[(-1)^(k-1)/(2*k-1), {k, 50000}], 10, 100]] (* _Paolo Xausa_, May 11 2024 *)
%Y A216543 Cf. A000796, A216542, A013706, A216543, A216544, A216545, A013705, A216546, A216547, A216548.
%Y A216543 Cf. also A195793.
%K A216543 nonn,cons,easy
%O A216543 1,1
%A A216543 _N. J. A. Sloane_, Sep 08 2012