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 A231181 #22 Aug 21 2019 16:17:41
%S A231181 1,1,5,6,20,27,75,110,275,429,1001,1637,3639,6172,13243,23104,48280,
%T A231181 86090,176341,319792,645150,1185305,2363596,4386331,8669142,16212913,
%U A231181 31825005,59873834,116914020,220964744,429737220,815057639,1580244061
%N A231181 Expansion of 1/(1 - x - 4*x^2 + 3*x^3 + 3*x^4 - x^5).
%C A231181 This sequence is fundamental for the coefficient sequences for the nonnegative powers of rho(11) = 2*cos(Pi/n) (length ration (smallest diagonal)/side in the regular 11-gon (Hendecagon)) when written in the power basis of the degree 5 number field Q(rho(11)). See A187360 for the minimal polynomial of rho(11) which is C(11, x) = x^5 - x^4 - 4*x^3 + 3*x^2 + 3*x - 1. See A231182-5 for these coefficient sequences.
%H A231181 Michael De Vlieger, <a href="/A231181/b231181.txt">Table of n, a(n) for n = 0..3532</a>
%H A231181 Genki Shibukawa, <a href="https://arxiv.org/abs/1907.00334">New identities for some symmetric polynomials and their applications</a>, arXiv:1907.00334 [math.CA], 2019.
%H A231181 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,4,-3,-3,1).
%F A231181 G.f.: 1/(1 - x - 4*x^2 + 3*x^3 + 3*x^4 - x^5).
%F A231181 a(n) = a(n-1) + 4*a(n-2) - 3*a(n-3) - 3*a(n-4) + a(n-5) for n>=0, with a(-5)=1, a(-4)=a(-3)=a(-2)=a(-1)=0.
%t A231181 CoefficientList[Series[1/(1-x-4x^2+3x^3+3x^4-x^5),{x,0,50}],x] (* or *) LinearRecurrence[{1,4,-3,-3,1},{1,1,5,6,20},50] (* _Harvey P. Dale_, Nov 13 2013 *)
%Y A231181 Cf. A231182, A231183, A231184, A231185.
%K A231181 nonn,easy
%O A231181 0,3
%A A231181 _Wolfdieter Lang_, Nov 05 2013