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.
Number triangle begins 1, 0, 1, 1, 0, 1, 1, 3, 0, 1, 5, 3, 5, 0, 1, 11, 18, 5, 7, 0, 1, 41, 39, 35, 7, 9, 0, 1, 120, 157, 75, 56, 9, 11, 0, 1
a:=[1,1,0,-3];; for n in [5..40] do a[n]:=3*a[n-1]-5*a[n-2]+3*a[n-3]-a[n-4]; od; a; # G. C. Greubel, Aug 08 2019
R:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1-2*x+2*x^2-x^3)/(1-3*x+5*x^2-3*x^3+x^4) )); // G. C. Greubel, Aug 08 2019
seq(coeff(series((1-2*x+2*x^2-x^3)/(1-3*x+5*x^2-3*x^3+x^4), x, n+1), x, n), n = 0 .. 40); # G. C. Greubel, Aug 08 2019
LinearRecurrence[{3,-5,3,-1}, {1,1,0,-3}, 40] (* G. C. Greubel, Aug 08 2019 *)
my(x='x+O('x^40)); Vec((1-2*x+2*x^2-x^3)/(1-3*x+5*x^2-3*x^3+x^4)) \\ G. C. Greubel, Aug 08 2019
def A123879_list(prec): P.= PowerSeriesRing(ZZ, prec) return P((1-2*x+2*x^2-x^3)/(1-3*x+5*x^2-3*x^3+x^4)).list() A123879_list(40) # G. C. Greubel, Aug 08 2019
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