OFFSET
0,2
FORMULA
D-finite with recurrence: n*a(n) +2*(-2*n+23)*a(n-1)=0. - R. J. Mathar, Jan 17 2020
From Amiram Eldar, Mar 25 2022: (Start)
a(n) = (-4)^n*binomial(21/2, n).
Sum_{n>=0} 1/a(n) = 406240/415701 - 46*Pi/(3^13*sqrt(3)).
Sum_{n>=0} (-1)^n/a(n) = 728323714975904/710426513671875 - 92*log(phi)/(5^12*sqrt(5)), where phi is the golden ratio (A001622). (End)
MATHEMATICA
CoefficientList[Series[Surd[(1-4x)^21, 2], {x, 0, 30}], x] (* Harvey P. Dale, Feb 25 2020 *)
CROSSREFS
KEYWORD
sign
AUTHOR
STATUS
approved