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

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, 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, 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

Offset

1,1

Comments

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

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.

Index entries for linear recurrences with constant coefficients.

Example

3.14157265358979523846264238327950410419716662937511592517489...

Mathematica

First[RealDigits[4*Sum[(-1)^(k-1)/(2*k-1), {k, 50000}], 10, 100]] (* Paolo Xausa, May 11 2024 *)

Crossrefs

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

Cf. also A195793.

Sequence in context: A358919 A354617 A324242 * A379324 A152040 A013705

Adjacent sequences: A216540 A216541 A216542 * A216544 A216545 A216546

Keyword

nonn,cons,easy

Author

N. J. A. Sloane, Sep 08 2012

Status

approved