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A008545 Quadruple factorial numbers: Product_{k=0..n-1} (4*k + 3). 39
1, 3, 21, 231, 3465, 65835, 1514205, 40883535, 1267389585, 44358635475, 1729986783525, 74389431691575, 3496303289504025, 178311467764705275, 9807130727058790125, 578620712896468617375, 36453104912477522894625, 2442358029135994033939875 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n-1), n >= 1, enumerates increasing plane (a.k.a. ordered) trees with n vertices (one of them a root labeled 1) with one version of a vertex with out-degree r=0 (a leaf or a root) and each vertex with out-degree r >= 1 comes in binom(r+2,2) types (like a binom(r+2,2)-ary vertex). See the increasing tree comments under A001498. For example, a(1)=3 from the three trees with n=2 vertices (a root (out-degree r=1, label 1) and a leaf (r=0), label 2). There are three such trees because of the three types of out-degree r=1 vertices. - Wolfdieter Lang, Oct 05 2007 [corrected by Karen Yeats, Jun 17 2013]

a(n) is the product of the positive integers less than or equal to 4n that have modulo 4 = 3. - Peter Luschny, Jun 23 2011

LINKS

T. D. Noe, Table of n, a(n) for n = 0..100

W. Lang, On generalizations of Stirling number triangles, J. Integer Seqs., Vol. 3 (2000), #00.2.4.

FORMULA

a(n) = 3*A034176(n) = (4*n-1)(!^4), n >= 1, a(0) := 1.

E.g.f.: (1-4*x)^(-3/4).

a(n) ~ 2^(1/2)*Pi^(1/2)*Gamma(3/4)^-1*n^(1/4)*2^(2*n)*e^-n*n^n*{1 - 1/96*n^-1 + ...}. - Joe Keane (jgk(AT)jgk.org), Nov 23 2001

G.f.: 1/(1-3x/(1-4x/(1-7x/(1-8x/(1-11x/(1-12x/(1-15x/(1-16x/(1-19x/(1-20x/(1-23x/(1-24x/(1-... (continued fraction). - Paul Barry, Dec 03 2009

a(n) = (-1)^n*Sum_{k=0..n} 4^k*s(n+1,n+1-k), where s(n,k) are the Stirling numbers of the first kind, A048994. - Mircea Merca, May 03 2012

a(n) + (-4*n + 1)*a(n-1) = 0. - R. J. Mathar, Dec 04 2012

G.f.: 1/x - G(0)/(2*x), where G(k)= 1 + 1/(1 - x*(4*k-1)/(x*(4*k-1) + 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 04 2013

a(-n) = (-1)^n / A007696(n). - Michael Somos, Jan 17 2014

G.f.: 1/(1 - b(1)*x / (1 - b(2)*x / ...)) where b = A014601. - Michael Somos, Jan 17 2014

a(n) = 4^n * GAMMA(n+3/4) / GAMMA(3/4). - Vaclav Kotesovec, Jan 28 2015

a(n) = A225471(n, 0), n >= 0. a(n) = sigma[4,3]^{(n)}_n, with the elementary symmetric function sigma[4,3]^{n}_n of degree n of the n numbers 3, 7, 11, ..., (3 + 4*(n-1)), and sigma[4,3]^{n}_0 := 1. See the formula given in the name. - Wolfdieter Lang, May 29 2017

EXAMPLE

G.f. = 1 + 3*x + 21*x^2 + 231*x^3 + 3465*x^4 + 65835*x^5 + 1514205*x^6 + ...

a(3) = sigma[4,3]^{3}_3 = 3*7*11 = 231. See the name. - Wolfdieter Lang, May 29 2017

MAPLE

f := n->product( (4*k-1), k=0..n);

A008545 := n -> mul(k, k = select(k-> k mod 4 = 3, [$1 .. 4*n])): seq(A008545(n), n=0..15); # Peter Luschny, Jun 23 2011

MATHEMATICA

s=1; lst={s}; Do[s+=n*s; AppendTo[lst, s], {n, 2, 5!, 4}]; lst (* Vladimir Joseph Stephan Orlovsky, Nov 08 2008 *)

FoldList[Times, 1, 4*Range[0, 20]+3] (* Harvey P. Dale, Jan 19 2013 *)

a[ n_] := Pochhammer[ 3/4, n] 4^n; (* Michael Somos, Jan 17 2014 *)

a[ n_] := If[n < 0, 1 / Product[ -k, {k, 1, -4 n - 3, 4}], Product[ k, {k, 3, 4 n - 1, 4}]]; (* Michael Somos, Jan 17 2014 *)

PROG

(PARI) a(n)=prod(k=0, n-1, 4*k+3) \\ Charles R Greathouse IV, Jun 23 2011

(Haskell)

a008545 n = a008545_list !! n

a008545_list = scanl (*) 1 a004767_list

-- Reinhard Zumkeller, Oct 25 2013

(PARI) {a(n) = if( n<0, 1 / prod(k=1, -n, 3 - 4*k), prod(k=1, n, 4*k - 1))}; /* Michael Somos, Jan 17 2014 */

CROSSREFS

Cf. A004982, A001813, A047053, A051142, A254286.

a(n)= A000369(n+1, 1) (first column of triangle).

Partial products of A004767.

Cf. A007696, A014601, A225471 (first column).

Sequence in context: A074638 A097329 A119097 * A005373 A078586 A179331

Adjacent sequences:  A008542 A008543 A008544 * A008546 A008547 A008548

KEYWORD

nonn,easy,nice

AUTHOR

Joe Keane (jgk(AT)jgk.org)

STATUS

approved

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Last modified April 19 19:09 EDT 2019. Contains 322290 sequences. (Running on oeis4.)