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A110903
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Difference between the factorial of n and the double factorial of n.
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3
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0, 0, 0, 3, 16, 105, 672, 4935, 39936, 361935, 3624960, 39906405, 478955520, 6226885665, 87177646080, 1307672340975, 20922779566080, 355687393636575, 6402373519933440, 121645099754102925, 2432902004460748800, 51090942157960129425, 1124000727695858073600
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = n! - n!!.
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EXAMPLE
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a(7) = 7*6*5*4*3*2*1 - 7*5*3*1 = 4935.
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MATHEMATICA
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PROG
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(PARI) a(n)={n! - if(n%2, n!/((n\2)!*2^(n\2)), (n/2)!*2^(n/2))} \\ Andrew Howroyd, Jan 02 2020
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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