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A279886
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a(n) = A057863(n+1) * Sum_{k=0..n}(k! / (2*k+1)!!).
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1
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1, 4, 66, 7200, 6917400, 72442188000, 9822893856930000, 19942863749656848000000, 687732249521129504041350000000, 450437284567157389148103391935000000000, 6194243041031315772374678081343893262937500000000
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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(0) = 1, a(n) = a(n-1) * (2*n+1)!! + n! * A057863(n).
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MATHEMATICA
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Table[Product[(2 k - 1)!!, {k, n + 1}] Sum[(j!/(2 j + 1)!!), {j, 0, n}], {n, 0, 10}] (* Michael De Vlieger, Dec 22 2016 *)
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PROG
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(PARI) a(n) = prod(k=0, n, prod(i=0, k, 2*i+1))*sum(k=0, n, k!/prod(i=0, k, 2*i+1));
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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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