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 A290987 #25 Apr 13 2023 18:14:31
%S A290987 1,2,4,8,16,32,63,122,233,441,830,1557,2915,5451,10186,19026,35529,
%T A290987 66337,123849,231211,431631,805768,1504193,2807986,5241856,9785309,
%U A290987 18266848,34099850,63656272,118831031,221829087,414101780,773028830,1443059634,2693846606
%N A290987 Expansion of (1 - 2*x + x^2 - x^4 + x^3 + x^5)/((1 - x)^2*(1 - 2*x + x^3 - x^4)).
%H A290987 Robert Israel, <a href="/A290987/b290987.txt">Table of n, a(n) for n = 0..3684</a>
%H A290987 T. Langley, J. Liese, and J. Remmel, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Langley/langley2.html">Generating Functions for Wilf Equivalence Under Generalized Factor Order</a>, J. Int. Seq. 14 (2011) # 11.4.2, A(123;1,x).
%H A290987 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4,-5,1,3,-3,1).
%F A290987 a(n) = A059633(n+2) + A059633(n+3) - n.
%p A290987 f:= gfun:-rectoproc({a(n)-3*a(n+1)+3*a(n+2)+a(n+3)-5*a(n+4)+4*a(n+5)-a(n+6), a(0) = 1, a(1) = 2, a(2) = 4, a(3) = 8, a(4) = 16, a(5) = 32}, a(n),remember):
%p A290987 map(f, [$0..50]); # _Robert Israel_, Aug 16 2017
%t A290987 DeleteCases[#, 0] &@ CoefficientList[Series[(1-2x+x^2-x^4+x^3+x^5)/((1-x)^2*(1-2x +x^3-x^4)), {x,0,34}], x] (* _Michael De Vlieger_, Aug 16 2017 *)
%t A290987 LinearRecurrence[{4,-5,1,3,-3,1}, {1,2,4,8,16,32}, 40] (* _Vincenzo Librandi_, Aug 17 2017 *)
%o A290987 (Magma) I:=[1,2,4,8,16,32]; [n le 6 select I[n] else 4*Self(n-1)-5*Self(n-2) +Self(n-3)+3*Self(n-4)-3*Self(n-5)+Self(n-6): n in [1..40]]; // _Vincenzo Librandi_, Aug 17 2017
%o A290987 (PARI) Vec((1-2*x+x^2-x^4+x^3+x^5)/((1-x)^2*(1-2*x+x^3-x^4)) + O(x^50)) \\ _Michel Marcus_, Aug 17 2017
%o A290987 (SageMath)
%o A290987 def A290987_list(prec):
%o A290987 P.<x> = PowerSeriesRing(ZZ, prec)
%o A290987 return P( (1-2*x+x^2-x^4+x^3+x^5)/((1-x)^2*(1-2*x+x^3-x^4)) ).list()
%o A290987 A290987_list(50) # _G. C. Greubel_, Apr 12 2023
%Y A290987 Cf. A059633, A290986, A290989.
%K A290987 nonn,easy
%O A290987 0,2
%A A290987 _R. J. Mathar_, Aug 16 2017