cp's OEIS Frontend

A369186 The denominators of a series that converges to the Dottie Number (A003957).

%I A369186 #23 May 30 2025 03:32:41
%S A369186 1,3,12,260,5720,314248,17255072,1769058016,181357735680,
%T A369186 29880655637760,4923158441956352,1189676108826729472,
%U A369186 287484053261423565824,95784714773484796761088,31913810779214031287095296,2804341960426298188743438336,1232120770958699233546743119872
%N A369186 The denominators of a series that converges to the Dottie Number (A003957).
%C A369186 Whittaker's root series formula is applied to 1 - x - x^2/2! + x^4/4! - x^6/6! + ..., which is the Taylor expansion of cos(x) - x. The following infinite series for the Dottie number (D) is obtained: D = 1/1 - 1/3 + 1/12 - 3/260 + 1/5720 + 205/314248 - 4439/17255072 ... . The sequence is formed by the denominators of the series.
%H A369186 E. T. Whittaker and G. Robinson, <a href="https://archive.org/details/calculusofobserv031400mbp/page/n139/mode/2up">The Calculus of Observations</a>, London: Blackie & Son, Ltd. 1924, pp. 120-123.
%F A369186 a(1)=1;
%F A369186 for n > 1, a(n) is the denominator of the simplified fraction -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n+1)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n+1)))), where c(0)=1, c(1)=-1, c(2)=-1/2!, c(3)=0, c(4)=1/4!, c(5)=0, c(6)=-1/6!, and c(n) is the coefficient of x^n in the Taylor expansion of cos(x)-x.
%e A369186 a(1) is the denominator of -1/-1 = 1/1.
%e A369186 a(2) is the denominator of simplified -(-1/2!)/(-1* det ToeplitzMatrix((-1,1),(-1,-1/2!))) = (1/2)/(-3/2) = -1/3.
%e A369186 a(3) is the denominator of the simplified -det ToeplitzMatrix((-1/2!,-1),(-1/2!,0))/(det ToeplitzMatrix((-1,1),(-1,-1/2!))*det ToeplitzMatrix((-1,1,0),(-1,-1/2!,0))) = -(1/4)/((3/2)*-2) = 1/12.
%Y A369186 Cf. A003957.
%K A369186 nonn
%O A369186 1,2
%A A369186 _Raul Prisacariu_, Jan 15 2024
%E A369186 a(8)-a(17) from _Chai Wah Wu_, Feb 10 2024