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 A228706 #24 Sep 08 2022 08:46:05
%S A228706 1,1,1,5,11,14,18,30,45,55,67,91,119,140,164,204,249,285,325,385,451,
%T A228706 506,566,650,741,819,903,1015,1135,1240,1352,1496,1649,1785,1929,2109,
%U A228706 2299,2470,2650,2870,3101,3311,3531,3795,4071,4324,4588,4900,5225,5525
%N A228706 Expansion of (1 - 3*x + 5*x^2 - 3*x^3 + x^4)/((1-x)^4*(1+x^2)^2).
%C A228706 A159914 and A228705 both satisfy the same recurrence relation, and both count (n-3)-element subsets of {1..n} having even resp. odd sum. Is there a similar subset-counting interpretation for this sequence? - _M. F. Hasler_, Jun 22 2018
%H A228706 Vincenzo Librandi, <a href="/A228706/b228706.txt">Table of n, a(n) for n = 0..1000</a>
%H A228706 E. Kirkman, J. Kuzmanovich and J. J. Zhang, <a href="http://arxiv.org/abs/1305.3973">Invariants of (-1)-Skew Polynomial Rings under Permutation Representations</a>, arXiv preprint arXiv:1305.3973 [math.RA], 2013. See Example 5.6.
%H A228706 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (4,-8,12,-14,12,-8,4,-1).
%F A228706 a(n) = (n+2)*(2*(n+1)*(n+3)+9*(1+(-1)^n)*i^(n*(n+1)))/48, where i=sqrt(-1). [_Bruno Berselli_, Sep 07 2013]
%t A228706 CoefficientList[Series[(1 - 3 x + 5 x^2 - 3 x^3 + x^4) / ((1 - x)^4 (1 + x^2)^2), {x, 0, 50}], x] (* _Vincenzo Librandi_, Sep 07 2013 *)
%o A228706 (Magma) m:=50; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1-3*x+5*x^2-3*x^3+x^4)/((1-x)^4*(1+x^2)^2)); // _Vincenzo Librandi_, Sep 07 2013
%o A228706 (PARI) Vec((1-3*x+5*x^2-3*x^3+x^4)/((1-x)^4*(1+x^2)^2)+O(x^99)) \\ _M. F. Hasler_, Jun 22 2018
%Y A228706 Cf. A159914, A228705.
%K A228706 nonn,easy
%O A228706 0,4
%A A228706 _N. J. A. Sloane_, Sep 06 2013