A014297 a(n) = n! * C(n+2, 2) * 2^(n+1).

2, 12, 96, 960, 11520, 161280, 2580480, 46448640, 928972800, 20437401600, 490497638400, 12752938598400, 357082280755200, 10712468422656000, 342798989524992000, 11655165643849728000, 419585963178590208000, 15944266600786427904000, 637770664031457116160000

Offset

0,1

Comments

Partition the set {1,2,...,n+2} into an even number of subsets. Arrange (linearly order) the elements within each subset and then arrange the subsets. - Geoffrey Critzer, Mar 03 2010

Links

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 506

Alexsandar Petojevic, The Function vM_m(s; a; z) and Some Well-Known Sequences, Journal of Integer Sequences, Vol. 5 (2002), Article 02.1.7.

Formula

a(n) = Sum_{k=0..n} (n+2)!*C(n,k).

Prepend the sequence with 1,0, then e.g.f. is (1-x)^2/(1-2*x). - Geoffrey Critzer, Mar 03 2010

E.g.f.: 2/(1-2*x)^3. - R. J. Mathar, Nov 27 2011

a(n) = 2*A051578(n). - R. J. Mathar, Apr 26 2017

a(n) = (n+2)! * 2^n. - Joerg Arndt, May 05 2019

From Amiram Eldar, Jul 04 2020: (Start)

Sum_{n>=0} 1/a(n) = 4*sqrt(e) - 6.

Sum_{n>=0} (-1)^n/a(n) = 4/sqrt(e) - 2. (End)

Maple

seq(count(Permutation(n+1))*count(Composition(n)), n=1..17); # Zerinvary Lajos, Oct 16 2006

Mathematica

Drop[CoefficientList[Series[(1-x)^2/(1-2x), {x, 0, 20}], x]* Table[n!, {n, 0, 20}], 2] (* Geoffrey Critzer, Mar 03 2010 *)
Part[#, Range[1, Length[#], 1]]&@(Array[#!&, Length[#], 0]*#)&@CoefficientList[Series[2/(1 - 2*x)^3, {x, 0, 20}], x]// ExpandAll (* Vincenzo Librandi, Jan 04 2013 - after Olivier Gérard in A213068 *)
Table[n!Binomial[n+2, 2]2^(n+1), {n, 0, 30}] (* Harvey P. Dale, Dec 27 2022 *)

Prog

(PARI) a(n) = (n+2)!*2^n; \\ Joerg Arndt, May 05 2019
(Magma) [2^n*Factorial(n+2): n in [0..20]]; // G. C. Greubel, May 05 2019
(Sage) [2^n*factorial(n+2) for n in (0..20)] # G. C. Greubel, May 05 2019
(GAP) List([0..20], n-> 2^n*Factorial(n+2)) # G. C. Greubel, May 05 2019

Crossrefs

Essentially the same as A052564.

Cf. A088312.

Sequence in context: A153231 A365282 A052564 * A193425 A206855 A219119

Adjacent sequences: A014294 A014295 A014296 * A014298 A014299 A014300

Keyword

nonn,easy

Author

Emeric Deutsch

Status

approved