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A224514
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Expansion of (1-x)*(1-3*x)*(1-3*x+x^2)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).
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2
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1, 2, 6, 20, 70, 251, 911, 3327, 12190, 44744, 164407, 604487, 2223504, 8181175, 30108147, 110820165, 407946421, 1501844193, 5529362694, 20358557249, 74961030414, 276017648570, 1016360893036, 3742540945813, 13781324308298, 50748099850042
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OFFSET
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0,2
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COMMENTS
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A diagonal of the square array A223968.
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LINKS
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FORMULA
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G.f.: (1-x)*(1-3*x)*(1-3*x+x^2)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).
a(n) = 9*a(n-1) - 28*a(n-2) + 35*a(n-3) - 15*a(n-4) + a(n-5) with a(0) = 1, a(1) = 2, a(2) = 6, a(3) = 20, a(4) = 70.
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MATHEMATICA
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LinearRecurrence[{9, -28, 35, -15, 1}, {1, 2, 6, 20, 70, 251, 911, 3327, 12190, 44744, 164407, 604487, 2223504, 8181175}, 40] (* Harvey P. Dale, Apr 24 2016 *)
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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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EXTENSIONS
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STATUS
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approved
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