This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A020931 #16 Mar 25 2022 09:14:29
%S A020931 1,-38,646,-6460,41990,-184756,554268,-1108536,1385670,-923780,184756,
%T A020931 33592,16796,12920,12920,15504,21318,32604,54340,97240,184756,369512,
%U A020931 772616,1679600,3779100,8767512,20907144,51106352,127765880,326023280,847660528,2242198816
%N A020931 Expansion of (1-4*x)^(19/2).
%F A020931 D-finite with recurrence: n*a(n) +2*(-2*n+21)*a(n-1)=0. - _R. J. Mathar_, Jan 17 2020
%F A020931 From _Amiram Eldar_, Mar 25 2022: (Start)
%F A020931 a(n) = (-4)^n*binomial(19/2, n).
%F A020931 Sum_{n>=0} 1/a(n) = 45052/46189 + 14*Pi/(3^11*sqrt(3)).
%F A020931 Sum_{n>=0} (-1)^n/a(n) = 6955761045148/6765966796875 - 84*log(phi)/(5^11*sqrt(5)), where phi is the golden ratio (A001622). (End)
%t A020931 CoefficientList[Series[(1-4x)^(19/2),{x,0,30}],x] (* _Harvey P. Dale_, Jul 03 2013 *)
%Y A020931 Cf. A001622, A002420, A002421, A002422, A002423, A002424, A020923, A020925, A020927, A020929.
%K A020931 sign
%O A020931 0,2
%A A020931 _N. J. A. Sloane_