%I #13 Mar 25 2022 09:14:35

%S 1,-42,798,-9044,67830,-352716,1293292,-3325608,5819814,-6466460,

%T 3879876,-705432,-117572,-54264,-38760,-36176,-40698,-52668,-76076,

%U -120120,-204204,-369512,-705432,-1410864,-2939300,-6348888,-14162904,-32522224,-76659528,-185040240

%N Expansion of (1-4*x)^(21/2).

%F D-finite with recurrence: n*a(n) +2*(-2*n+23)*a(n-1)=0. - _R. J. Mathar_, Jan 17 2020

%F From _Amiram Eldar_, Mar 25 2022: (Start)

%F a(n) = (-4)^n*binomial(21/2, n).

%F Sum_{n>=0} 1/a(n) = 406240/415701 - 46*Pi/(3^13*sqrt(3)).

%F Sum_{n>=0} (-1)^n/a(n) = 728323714975904/710426513671875 - 92*log(phi)/(5^12*sqrt(5)), where phi is the golden ratio (A001622). (End)

%t CoefficientList[Series[Surd[(1-4x)^21,2],{x,0,30}],x] (* _Harvey P. Dale_, Feb 25 2020 *)

%Y Cf. A001622, A002420, A002421, A002422, A002423, A002424, A020923, A020925, A020927, A020929, A020931.

%K sign

%O 0,2

%A _N. J. A. Sloane_.