OFFSET
0,1
COMMENTS
Machin's formula: Pi/4 = 4*atan(1/5) - atan(1/239).
Sum_{n>=0} 1/a(n) = Pi/16 = atan(1/5) - (1/4)*atan(1/239).
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..415
X. Gourdon and P. Sebah, Collection of series for Pi
FORMULA
a(2n) = (2*n+1)*5^(2*n+1)*(-1)^n,
a(2n+1) = -4*(2*n+1)*239^(2*n+1)*(-1)^n.
G.f.: 5*(1-25*x^2)/(1+25*x^2)^2 - 956*x*(1-57121*x^2)/(1+57121*x^2)^2
MAPLE
seq(coeff(series(5*(1-(5*x)^2)/(1+(5*x)^2)^2 - 4*239*x*(1-(239*x)^2)/(1+(239*x)^2)^2, x, n+1), x, n), n = 0..15); # G. C. Greubel, Aug 26 2019
MATHEMATICA
CoefficientList[Series[5*(1-(5*x)^2)/(1+(5*x)^2)^2 - 4*239*x*(1-(239*x)^2)/(1+(239*x)^2)^2, {x, 0, 15}], x] (* G. C. Greubel, Aug 26 2019 *)
PROG
(PARI) my(x='x+O('x^15)); Vec(5*(1-(5*x)^2)/(1+(5*x)^2)^2 - 4*239*x*(1-(239*x)^2)/(1+(239*x)^2)^2) \\ G. C. Greubel, Aug 26 2019
(Magma) R<x>:=PowerSeriesRing(Integers(), 15); Coefficients(R!( 5*(1-(5*x)^2)/(1+(5*x)^2)^2 - 4*239*x*(1-(239*x)^2)/(1+(239*x)^2)^2 )); // G. C. Greubel, Aug 26 2019
(Sage)
def A077952_list(prec):
P.<x> = PowerSeriesRing(ZZ, prec)
return P( 5*(1-(5*x)^2)/(1+(5*x)^2)^2 - 4*239*x*(1-(239*x)^2)/(1+(239*x)^2)^2 ).list()
A077952_list(15) # G. C. Greubel, Aug 26 2019
(GAP)
a:= function(n)
if n mod 2=0 then return (-1)^(n/2)*(n+1)*5^(n+1);
else return -4*(-1)^((n-1)/2)*n*(239)^n;
fi;
end;
List([0..15], n-> a(n) ); # G. C. Greubel, Aug 26 2019
CROSSREFS
KEYWORD
frac,sign,easy
AUTHOR
Jaume Oliver Lafont, Feb 27 2009
EXTENSIONS
More terms from Colin Barker, Aug 07 2013
STATUS
approved