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A217777
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Expansion of (1+x)*(1+2*x)*(1-x)/(1-5*x^2+5*x^4).
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4
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1, 2, 4, 8, 15, 30, 55, 110, 200, 400, 725, 1450, 2625, 5250, 9500, 19000, 34375, 68750, 124375, 248750, 450000, 900000, 1628125, 3256250, 5890625, 11781250, 21312500, 42625000, 77109375, 154218750, 278984375, 557968750, 1009375000, 2018750000, 3651953125
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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) = sum(A217770(n-k,k), 0<=k<=n).
a(n) = 5*a(n-2) - 5*a(n-4) for n>=4, a(0) = 1, a(1) = 2, a(2) = 4, a(3) = 8.
G.f.: (1+x)*(1+2*x)*(1-x)/(1-5*x^2+5*x^4).
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PROG
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(PARI) Vec((1+x)*(1+2*x)*(1-x)/(1-5*x^2+5*x^4)+O(x^66)) /* Joerg Arndt, Mar 29 2013 */
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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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