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1, 7, 44, 262, 1504, 8416, 46208, 250016, 1337088, 7083264, 37229568, 194383360, 1009172480, 5213634560, 26819756032, 137445318656, 702021435392, 3574958587904, 18156130926592, 91985567678464, 465004476235776, 2345955741401088, 11813573860786176
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: -(((1 + x) (-1 + 2 x + 2 x^2))/(-1 + 4 x + 4 x^2)^2).
a(n) = 8*a(n-1) - 8*a(n-2) - 32*a(n-3) - 16*a(n-4) for n >= 5.
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MATHEMATICA
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z = 60; s = x + x^2; p = (1 - 4 s)^2;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A019590 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A291387 *)
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PROG
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(GAP)
a:=8*[1, 7, 44, 262];; for n in [5..10^2] do a[n]:=8*a[n-1]+-8*a[n-2]-32*a[n-3]-16*a[n-4]; od;
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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