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 A197131 #15 Jul 22 2025 12:53:16
%S A197131 4,46,544,7216,108096,1816704,33951744,699512832,15765626880,
%T A197131 386046443520,10208951009280,290039357767680,8811722692362240,
%U A197131 285113464809062400,9789232245217689600,355501479519741542400,13615286053738276454400,548476851979845579571200
%N A197131 Sum of the reflection (absolute) lengths of all elements in the Coxeter group of type D_n.
%D A197131 P. Renteln, The distance spectra of Cayley graphs of Coxeter groups, Discrete Math., 311 (2011), 738-755.
%H A197131 B. Foster-Greenwood, C. Kriloff, <a href="http://arxiv.org/abs/1502.07392">Spectra of Cayley Graphs of Complex Reflection Groups</a>, arXiv preprint arXiv:1502.07392, 2015
%F A197131 a(n)=Sum_{w in W(D_n)} l_T(w)=|W(D_n)|Sum_{i=1}^n (d_i-1)/d_i=2^(n-1)*n!*(1/2+3/4+...+(2n-3)/(2n-2)+(n-1)/n) where T=all reflections in W(D_n), l_T(1)=0 and otherwise l_T(w)=min{k|w=t_1*...*t_k for t_i in T}, and d_1,...,d_n are the degrees of W(D_n)
%e A197131 a(3)=46 because W(D_3)=W(A_3) and in sequence A067318, a(3)=46.
%p A197131 seq(2^(n-1)*factorial(n)*(add((2*k-1)/(2*k), k=1..n-1)+(n-1)/n), n=2..100);
%t A197131 Table[2^(n-1)*Factorial[n]*(Sum[(2*k-1)/(2*k),{k,1,n-1}]+(n-1)/n), {n,2,100}]
%o A197131 (Sage)
%o A197131 [2^(n-1)*factorial(n)*(sum([(2*k-1)/(2*k) for k in [1..n-1]])+(n-1)/n) for n in [2..100]]
%Y A197131 Cf. A067318, A197130
%K A197131 easy,nonn
%O A197131 2,1
%A A197131 _Cathy Kriloff_, Oct 10 2011