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A360219
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a(n) = Sum_{k=0..floor(n/4)} (-1)^k * binomial(n-3*k,k) * binomial(2*(n-3*k),n-3*k).
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5
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1, 2, 6, 20, 68, 240, 864, 3152, 11616, 43136, 161152, 604992, 2280416, 8624832, 32714688, 124399488, 474066560, 1810053120, 6922776576, 26517173760, 101710338048, 390603984896, 1501732753408, 5779500226560, 22263437981184, 85835254221824, 331193445626880
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OFFSET
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0,2
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COMMENTS
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Diagonal of rational function 1/(1 - x - y + x^4*y^3). - Seiichi Manyama, Mar 23 2023
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LINKS
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FORMULA
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G.f.: 1/sqrt(1 - 4*x*(1 - x^3)).
n*a(n) = 2*(2*n-1)*a(n-1) - 2*(2*n-4)*a(n-4).
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MAPLE
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add((-1)^k*binomial(n-3*k, k)*binomial(2*(n-3*k), n-3*k), k=0..n/3) ;
end proc:
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PROG
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(PARI) a(n) = sum(k=0, n\4, (-1)^k*binomial(n-3*k, k)*binomial(2*(n-3*k), n-3*k));
(PARI) my(N=30, x='x+O('x^N)); Vec(1/sqrt(1-4*x*(1-x^3)))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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