A216545 - OEIS

A216545

Decimal expansion of 2*Sum_{k=1..500000} (-1)^(k-1)/(2k-1).

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, 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, 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

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OFFSET

1,2

COMMENTS

An approximation to Pi/2.

LINKS

Table of n, a(n) for n=1..125.

J. M. Borwein, P. B. Borwein and K. Dilcher, Pi, Euler numbers and asymptotic expansions, Amer. Math. Monthly, 96 (1989), 681-687.

J. M. Borwein and R. M. Corless, Review of "An Encyclopedia of Integer Sequences" by N. J. A. Sloane and Simon Plouffe, SIAM Review, 38 (1996), 333-337.

EXAMPLE

1.57079532679489662023132169163475144209864569968755152548747...

CROSSREFS