OFFSET
0,1
COMMENTS
Asymptotic density of the even squarefree numbers (A039956). - Amiram Eldar, May 22 2020
REFERENCES
C. F. Gauss, Disquisitiones Arithmeticae, Yale, 1965; see p. 360.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..3000
FORMULA
Equals 1/(3*zeta(2)). - Michel Marcus, Jun 13 2017
Equals -Sum_{k>=1} mu(2*k)/(2*k)^2, where mu is the Möbius function (A008683). - Amiram Eldar, Jul 31 2020
EXAMPLE
.20264236728467554288775892641945527780871754934449309769121...
MATHEMATICA
RealDigits[2/\[Pi]^2, 10, 100][[1]] (* Harvey P. Dale, Mar 16 2011 *)
PROG
(PARI) 2/Pi^2 \\ Charles R Greathouse IV, Mar 25 2014
CROSSREFS
KEYWORD
cons,nonn
AUTHOR
N. J. A. Sloane, Feb 19 2011
STATUS
approved