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A020773 Decimal expansion of 1/4. 4
2, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Also, decimal expansion of  1/2 * integral_0^infinity 1/cosh(Pi*x) dx. - Bruno Berselli, Mar 20 2013

In the complex plane, this purely real number gives the coordinates for the inward cusp of the main cardioid of the Mandelbrot set. - Alonso del Arte, Jun 05 2016

Equals the sum of the fractional parts of the odd-indexed zeta values [Adamchik]: Sum_{k>=1} [Zeta(2k+1)-1] = 1/4 = A002117-1 + A013663-1 + A013665-1 + ... - R. J. Mathar, Jan 13 2021

LINKS

Table of n, a(n) for n=0..98.

V. S. Adamchi and H. M. Srivastava, Some series of the zeta and related functions, Analysis (Munich) 18 (1998) 271-288, eq (1.7)

FORMULA

1/4 = Sum_{n >= 1} (-1)^(n+1)*n/(4*n^2-1). - Bruno Berselli, Sep 09 2020

MATHEMATICA

RealDigits[1/4, 10, 100][[1]] (* Alonso del Arte, Jun 05 2016 *)

PROG

(PARI) .25 \\ Charles R Greathouse IV, Apr 15 2015

CROSSREFS

Sequence in context: A252783 A192225 A020821 * A249422 A100085 A159986

Adjacent sequences:  A020770 A020771 A020772 * A020774 A020775 A020776

KEYWORD

nonn,cons,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified February 28 02:10 EST 2021. Contains 341695 sequences. (Running on oeis4.)