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A305693
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a(n) = binomial(4*n, 2*n) - 4*n*binomial(2*n-2, n-1).
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2
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1, 2, 54, 852, 12550, 183356, 2698108, 40090728, 600970566, 9074671980, 137844584020, 2104090834456, 32247569822364, 495918392331992, 7648690018326840, 118264579157865424, 1832624131015069254, 28453041434367110220, 442512540108817131364
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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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G.f.: sqrt(1 + sqrt(1 - 16*x))/sqrt(2*(1 - 16*x)) - 4*x*(1 - 2*x)/(1 - 4*x)^(3/2). - Ilya Gutkovskiy, Jun 08 2018
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PROG
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(PARI) {a(n) = binomial(4*n, 2*n)-4*n*binomial(2*n-2, n-1)}
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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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