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A047081
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a(n) = Sum_{k=0..n} T(n, k), array T as in A047080.
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9
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1, 2, 3, 6, 11, 20, 37, 68, 125, 230, 423, 778, 1431, 2632, 4841, 8904, 16377, 30122, 55403, 101902, 187427, 344732, 634061, 1166220, 2145013, 3945294, 7256527, 13346834, 24548655, 45152016, 83047505, 152748176, 280947697, 516743378, 950439251, 1748130326, 3215312955, 5913882532, 10877325813
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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 - x - x^2 - x^3).
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MATHEMATICA
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LinearRecurrence[{1, 1, 1}, {1, 2, 3}, 61] (* G. C. Greubel, Oct 31 2022 *)
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PROG
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(Magma) [n le 3 select n else Self(n-1) +Self(n-2) +Self(n-3): n in [1..60]]; // G. C. Greubel, Oct 31 2022
(SageMath)
@CachedFunction
def a(n): return (n+1) if (n<3) else a(n-1) +a(n-2) +a(n-3) # a = A047081
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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