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A027180
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a(n) = Sum_{0<=j<=i<=n} A027170(i, j).
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1
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1, 7, 27, 79, 199, 459, 1003, 2119, 4383, 8947, 18115, 36495, 73303, 146971, 294363, 589207, 1178959, 2358531, 4717747, 9436255, 18873351, 37747627, 75496267, 150993639, 301988479, 603978259, 1207957923, 2415917359, 4831836343, 9663674427, 19327350715
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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) = 18*2^n - 2*n^2 - 10*n - 17.
a(n) = 5*a(n-1)-9*a(n-2)+7*a(n-3)-2*a(n-4) for n>3.
G.f.: (1+x)^2 / ((1-x)^3*(1-2*x)).
(End)
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MATHEMATICA
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LinearRecurrence[{5, -9, 7, -2}, {1, 7, 27, 79}, 50] (* Harvey P. Dale, Jul 08 2019 *)
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PROG
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(PARI) Vec((1+x)^2/((1-x)^3*(1-2*x)) + O(x^40)) \\ Colin Barker, Feb 20 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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STATUS
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approved
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