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A303647
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a(n) = ceiling(a(n-1)/(2^(1/3)-1)+1), a(1)=1.
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2
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1, 5, 21, 82, 317, 1221, 4699, 18080, 69561, 267625, 1029641, 3961362, 15240637, 58635641, 225590199, 867918160, 3339160721, 12846826845, 49425880861, 190157283842, 731596320957, 2814686695261, 10829006332499, 41662675404240, 160289731905481, 616686228261665
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: x*(1 + x + x^2) / ((1 - x)*(1 - 3*x - 3*x^2 - x^3)).
a(n) = 4*a(n-1) - 2*a(n-3) - a(n-4) for n>4.
(End)
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MAPLE
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a := proc(n) option remember;
if n<1 then 0 else
if n=1 then 1 else ceil(a(n-1)/(2^(1/3)-1)+1)
end if end if end proc;
seq(a(n), n=0..10);
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MATHEMATICA
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Nest[Append[#, Ceiling[#[[-1]]/(2^(1/3) - 1) + 1]] &, {1}, 25] (* or *)
Rest@ CoefficientList[Series[x (1 + x + x^2)/((1 - x) (1 - 3 x - 3 x^2 - x^3)), {x, 0, 25}], x] (* Michael De Vlieger, Apr 28 2018 *)
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PROG
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(PARI) a(n) = if (n==1, 1, ceil(a(n-1)/(2^(1/3)-1)+1)); \\ Michel Marcus, Apr 28 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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