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A123385
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a(n) = (n!)^2/2.
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3
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2, 18, 288, 7200, 259200, 12700800, 812851200, 65840947200, 6584094720000, 796675461120000, 114721266401280000, 19387894021816320000, 3800027228275998720000, 855006126362099712000000
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OFFSET
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2,1
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LINKS
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FORMULA
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a(n) = Sum[Product[k, {k, i, n}]*a(i), {i, 0, n - 1}].
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MATHEMATICA
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f[0] = 0; f[1] = 1; f[n_] := f[n] = Sum[Product[k, {k, i, n}]*f[i], {i, 0, n - 1}] Table[f[n], {n, 0, 30}]
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PROG
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(PARI) for(n=2, 25, print1((n!)^2/2, ", ")) \\ G. C. Greubel, Oct 13 2017
(Magma) [(Factorial(n))^2/2: n in [2..25]]; // G. C. Greubel, Oct 13 2017
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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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