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A216546 Decimal expansion of Sum_{k=1..5000000} (-1)^(k-1)/(2k-1).

%I A216546 #25 Feb 04 2025 10:11:05
%S A216546 7,8,5,3,9,8,1,1,3,3,9,7,4,4,8,3,0,9,6,1,6,1,6,0,8,4,5,8,1,9,8,7,5,6,
%T A216546 9,6,0,4,9,2,9,2,3,4,9,8,4,6,8,2,6,4,5,5,2,4,3,7,3,5,4,5,5,5,7,6,9,5,
%U A216546 4,1,0,1,8,2,4,1,5,7,2,4,9,6,5,6,8,7,3,5,6,8,0,8,5,5,2,9,3,6,6,6,7,6,0,2,7,5,2,1,5,3,1,3,6,3,0,1,5,9,3,6,8,9,3,7
%N A216546 Decimal expansion of Sum_{k=1..5000000} (-1)^(k-1)/(2k-1).
%C A216546 An approximation to Pi/4. The constant is rational, by definition (a product of finitely many rational numbers).
%H A216546 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 A216546 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 A216546 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>.
%e A216546 0.7853981133974483096161608458198756960492923498468264552437...
%p A216546 Digits:=300; M:=5000000; add(evalf((-1)^(k-1)/(2*k-1)), k=1..M);
%t A216546 RealDigits[Total[Table[(-1)^(k-1)/(2k-1),{k,5*10^6}]],10,130][[1]] (* _Harvey P. Dale_, May 06 2015 *)
%Y A216546 Cf. A003881, A216542, A013706, A216543, A216544, A216545, A013705, A216546, A216547, A216548.
%Y A216546 Cf. also A195793.
%K A216546 nonn,cons,easy
%O A216546 0,1
%A A216546 _N. J. A. Sloane_, Sep 08 2012