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 A181876 #21 Sep 03 2018 22:05:14
%S A181876 1,1,1,1,2,1,1,1,4,2,1,2,1,8,2,2,1,2,1,1,8,4,1,1,4,2,1,32,16,8,1,2,1,
%T A181876 4,1,1,64,32,8,2,4,2,1,8,2,2,1,16,2,1,2,1,8,1,1,1,1,256,32,32,16,16,4,
%U A181876 4,2,1,8,4,1,1,512,256,64,16,32,16,8,1,2,1,16,1,4,1,1,64,4,2,4,2,2
%N A181876 Denominators of coefficient array of minimal polynomials of cos(2*Pi/n). Rising powers in x.
%C A181876 The corresponding numerator array is A181875(n,m).
%C A181876 The sequence of row lengths is d(n)+1, with d(n):=A023022(n), n >= 2, and d(1):=1: [2, 2, 2, 2, 3, 2, 4, 3, 4, 3, 6, 3, 7, 4, 5, 5, 9, 4, 10, 5, 7, ...].
%C A181876 For details on the monic, minimal degree rational polynomial with one of its zeros cos(2*Pi/n), n >= 1 (so-called minimal polynomial of cos(2*Pi/n)), see the array A181875(n,m) where also references are found.
%D A181876 See A181875.
%H A181876 See A181875.
%F A181876 a(n,m) = denominator([x^m]Psi(n,x)), with the minimal polynomial Psi(n,x) of cos(2*Pi/n), n >= 1. See A181875 for details and references.
%e A181876 [1,1], [1,1], [2,1], [1,1], [4,2,1], [2,1], [8,2,2,1], [2,1,1], [8,4,1,1], [4,2,1], ...
%t A181876 ro[n_] := Denominator[ cc = CoefficientList[ MinimalPolynomial[ Cos[2*Pi/n], x], x] ; cc/Last[cc]]; Flatten[Table[ro[n], {n, 1, 21}]] (* _Jean-François Alcover_, Sep 27 2011 *)
%Y A181876 Cf. A023022, A181875, A181877, A183918.
%K A181876 nonn,easy,tabf
%O A181876 1,5
%A A181876 _Wolfdieter Lang_, Jan 08 2011