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Decimal expansion of 2*Sum_{k=1..5000000} (-1)^(k-1)/(2k-1).
10

%I #23 Oct 06 2017 04:31:02

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

%C An approximation to Pi/2.

%H 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 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 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.

%e 1.57079622679489661923232169163975139209858469969365291048747...

%Y Cf. A000796, A216542, A013706, A216543, A216544, A216545, A013705, A216546, A216547, A216548.

%Y Cf. also A013707, A195793.

%K cons,nonn,easy

%O 1,2

%A _N. J. A. Sloane_, Sep 08 2012