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A049853
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a(n) = a(n-1) + Sum_{k=0..n-3} a(k) for n >= 2, a(0)=1, a(1)=2.
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4
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1, 2, 2, 3, 6, 11, 19, 33, 58, 102, 179, 314, 551, 967, 1697, 2978, 5226, 9171, 16094, 28243, 49563, 86977, 152634, 267854, 470051, 824882, 1447567, 2540303, 4457921, 7823106, 13728594, 24092003, 42278518, 74193627
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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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a(n) = 2*a(n-1) - a(n-2) + a(n-3); 3 initial terms required.
G.f.: (1 - x)*(1 + x) / (1 - 2*x + x^2 - x^3). - Colin Barker, Jun 17 2018
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MAPLE
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a := proc(n) option remember: if n<2 then n+1 else a(n-1) + add(a(k), k=0..n-3) fi end: seq(a(n), n=0..33); # Johannes W. Meijer, Jun 18 2018
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MATHEMATICA
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LinearRecurrence[{2, -1, 1}, {1, 2, 2}, 40] (* Harvey P. Dale, May 12 2022 *)
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PROG
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(Haskell)
a049853 n = a049853_list !! n
a049853_list = 1 : 2 : 2 : 3 :
zipWith (+) a049853_list
(zipWith (+) (drop 2 a049853_list) (drop 3 a049853_list))
(PARI) Vec((1 - x)*(1 + x) / (1 - 2*x + x^2 - x^3) + O(x^40)) \\ Colin Barker, Jun 17 2018
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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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