A216547 Decimal expansion of 2*Sum_{k=1..5000000} (-1)^(k-1)/(2k-1).

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, 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, 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

Offset: 1

Author

N. J. A. Sloane, Sep 08 2012

Keywords

• cons
• nonn
• easy

Comments

An approximation to Pi/2. The constant is rational, by definition (a product of finitely many rational numbers).

Examples

			1.57079622679489661923232169163975139209858469969365291048747...
		

Links

• 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, P. B. Borwein and K. Dilcher, Pi, Euler numbers and asymptotic expansions, in Pi: The Next Generation (2016) pp. 197-205.
• 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.
• Index entries for linear recurrences with constant coefficients.

Crossrefs

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

Cf. also A013707, A195793.