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A075092
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Sum of generalized tribonacci numbers (A001644) and reflected generalized tribonacci numbers (A073145).
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0
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6, 0, 2, 12, 6, 20, 50, 56, 134, 264, 402, 836, 1542, 2652, 5154, 9392, 16902, 31824, 58082, 106172, 197126, 360932, 662994, 1223784, 2245766, 4130520, 7606770, 13976436, 25711622, 47310252, 86978370, 160002656, 294324230, 541249952
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Conjecture: a(n) nonnegative.
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FORMULA
| a(n)=a(n-2)+4a(n-3)+a(n-4)-a(n-6), a(0)=6, a(1)=0, a(2)=2, a(3)=12, a(4)=6, a(5)=20. G.f.: (6 - 4*x^2 - 12*x^3 - 2*x^4)/(1 - x^2 - 4*x^3 - x^4 + x^6).
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MATHEMATICA
| CoefficientList[Series[(6 - 4*x^2 - 12*x^3 - 2*x^4)/(1 - x^2 - 4*x^3 - x^4 + x^6), {x, 0, 40}], x]
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CROSSREFS
| Cf. A001644, A073145, A075091.
Sequence in context: A195406 A021628 A201331 * A152244 A179641 A110993
Adjacent sequences: A075089 A075090 A075091 * A075093 A075094 A075095
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KEYWORD
| easy,nonn
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AUTHOR
| Mario Catalani (mario.catalani(AT)unito.it), Aug 31 2002
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