A127111 a(n) = (n+1)! - (n)!!.

0, 1, 4, 21, 112, 705, 4992, 40215, 362496, 3627855, 39912960, 478991205, 6226974720, 87178156065, 1307673722880, 20922787860975, 355687417774080, 6402373671268575, 121645100223037440, 2432902007521910925

Offset

0,3

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Formula

a(n) = A000142(n+1) - A006882(n). - Michel Marcus, Aug 15 2013

Maple

seq(factorial(n+1) - doublefactorial(n), n = 0..20); # G. C. Greubel, Jan 30 2020

Mathematica

Table[((n+1)!-(n)!!), {n, 0, 20}]

Prog

(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

Crossrefs

Sequence in context: A301972 A026335 A027909 * A270787 A190089 A349300

Adjacent sequences: A127108 A127109 A127110 * A127112 A127113 A127114

Keyword

easy,nonn

Author

Zerinvary Lajos, Mar 21 2007

Status

approved