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 A180056 The number of permutations of {1,2,...,2n} with n ascents. 8
 1, 1, 11, 302, 15619, 1310354, 162512286, 27971176092, 6382798925475, 1865385657780650, 679562217794156938, 301958232385734088196, 160755658074834738495566, 101019988341178648636047412, 73990373947612503295166622044, 62481596875767023932367207962680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Define the Eulerian numbers A(n,k) (see A008292) to be the number of permutations of {1,2,..,n} with k ascents: A(n,k) = Sum_{j=0..k} (-1)^j binomial(n+1,j)*(k-j+1)^n. Then a(n) = A(2*n,n) are the central Eulerian numbers. (Analogous to what are called the central binomial coefficients). LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 Digital Library of Mathematical Functions, Table 26.14.1 FORMULA a(n-1) = A025585(n)/(2*n). - Gary Detlefs, Nov 11 2011 a(n+1)/a(n) ~ 4*n^2. - Ran Pan, Oct 26 2015 a(n) ~ sqrt(3) * 2^(2*n+1) * n^(2*n) / exp(2*n). - Vaclav Kotesovec, Oct 16 2016 From Alois P. Heinz, Jul 21 2018: (Start) a(n) = ceiling(1/2 * (2n)! * [x^(2n) y^n] (exp(x)-y*exp(y*x))/(exp(y*x)-y*exp(x))). a(n) = (2n)! * [x^(2n) y^n] (1-y)/(1-y*exp((1-y)*x)). (End) MAPLE A180056 := proc(n) local j;   add((-1)^j*binomial(2*n+1, j)*(n-j+1)^(2*n), j=0..n) end: # A180056_list(m) returns [a_0, a_1, .., a_m] A180056_list :=   proc(m) local A, R, M, n, k;     R := 1; M := m + 1;     A := array([seq(1, n = 1..M)]);     for n from 2 to M do       for k from 2 to M do         if n = k then R := R, A[k] fi;         A[k] := n*A[k-1] + k*A[k]       od     od;   R end: MATHEMATICA A025585[n_] := Sum[(-1)^j*(n-j)^(2*n-1)*Binomial[2*n, j], {j, 0, n}]; a[0] = 1; a[n_] := A025585[n+1]/(2*n+2); Table[a[n], {n, 0, 13}] (* Jean-François Alcover, Jun 28 2013, after Gary Detlefs *) << Combinatorica`; Table[Combinatorica`Eulerian[2 n, n], {n, 0, 20}] (* Vladimir Reshetnikov, Oct 15 2016 *) PROG # Python def A180056_list(m): ....ret = [1] ....M = m + 1 ....A = [1 for i in range(0, M)] ....for n in range(2, M): ........for k in range(2, M): ............if n == k: ................ret.append(A[k]) ............A[k] = n*A[k-1] + k*A[k] ....return ret CROSSREFS A bisection of A006551. Cf. A008292, A025585, A303284, A303285, A303286, A303287. Sequence in context: A002114 A012192 A012079 * A172506 A250551 A001280 Adjacent sequences:  A180053 A180054 A180055 * A180057 A180058 A180059 KEYWORD nonn AUTHOR Peter Luschny, Aug 08 2010 EXTENSIONS Partially edited by N. J. A. Sloane, Aug 08 2010 STATUS approved

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Last modified September 22 22:42 EDT 2018. Contains 315270 sequences. (Running on oeis4.)