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A127111
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a(n) = (n+1)! - (n)!!.
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1
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0, 1, 4, 21, 112, 705, 4992, 40215, 362496, 3627855, 39912960, 478991205, 6226974720, 87178156065, 1307673722880, 20922787860975, 355687417774080, 6402373671268575, 121645100223037440, 2432902007521910925
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OFFSET
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0,3
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LINKS
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FORMULA
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MAPLE
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seq(factorial(n+1) - doublefactorial(n), n = 0..20); # G. C. Greubel, Jan 30 2020
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MATHEMATICA
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Table[((n+1)!-(n)!!), {n, 0, 20}]
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PROG
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(PARI) vector(21, n, my(m=n-1); if(m%2==0, (m+1)! - 2^(m/2)*(m/2)!, (m+1)! - m!/(2^((m-1)/2)*((m-1)/2)!)) ) \\ G. C. Greubel, Jan 30 2020
(Magma) DoubleFactorial:=func< n | &*[n..2 by -2] >;
[Factorial(n+1) - DoubleFactorial(n): n in [0..20]]; // G. C. Greubel, Jan 30 2020
(Sage) [factorial(n+1) - n.multifactorial(2) for n in (0..20)] # G. C. Greubel, Jan 30 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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STATUS
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approved
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