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A058562 Another 3-way generalization of series-parallel networks with n labeled edges. 7
0, 1, 3, 21, 243, 3933, 81819, 2080053, 62490339, 2166106509, 85092601707, 3735939709989, 181287330220467, 9634718677393917, 556569415611455931, 34723276781195740437, 2326773811332029313411, 166666995789875216053101, 12708546598923724476443403 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..360

O. Bodini, A. Genitrini, F. Peschanski and N. Rolin, Associativity for binary parallel processes, CALDAM 2015; [Slides]

FORMULA

E.g.f.: -3/2*LambertW(-2/3*exp(-2/3+1/3*x))-1. - Vladeta Jovovic, Jun 25 2007

E.g.f.: A(x) = Series_Reversion[ 3*log(1+x) - 2*x ]. [Paul D. Hanna, Aug 03 2008]

Let f(x) = (1+x)/(1-2*x). Let D be the operator g(x) -> d/dx(f(x)*g(x)). Then for n>=1, a(n) = D^(n-1)(1) evaluated at x = 0. - Peter Bala, Sep 05 2011

log(1 + A(x)) = x + 2*x^2/2! + 14*x^3/3! + 162*x^4/4! + ... is the e.g.f. for A201465. - Peter Bala, Jul 12 2012

a(n) = sum(k=0..n-1, (n+k-1)!*sum(j=0..k, 1/(k-j)!*sum(l=0..j, (3^(j-l)*(2)^l*(-1)^(l+j)*stirling1(n-l+j-1,j-l))/(l!*(n-l+j-1)!)))).  [Vladimir Kruchinin, Sep 26 2012]

G.f.: x/Q(0), where Q(k)= 1 - (k+1)*x - 2*x*(k+1)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, May 01 2013

a(n) ~ sqrt(3) * n^(n-1) / (2*exp(n) * (log(27/8)-1)^(n-1/2)). - Vaclav Kotesovec, Oct 05 2013

a(n) = a(n-1) + Sum_{j=1..n-1} binomial(n,j)*a(j)*a(n-j) for n>1. - Peter Luschny, May 24 2017

MAPLE

spec := [ N, {N=Union(Z, S, P, Q), S=Set(Union(Z, P, Q), card>=2), P=Set(Union(Z, S, Q), card>=2), Q=Set(Union(Z, S, P), card>=2)}, labeled ]; [seq(combstruct[count](spec, size=n), n=0..40)]; # N=A058562, S=A058575

# Alternatively:

A058562_list := proc(len) local A, n; A[0] := 0; A[1] := 1; for n from 2 to len do

A[n] := A[n-1] + add(binomial(n, j)*A[j]*A[n-j], j=1..n-1) od:

convert(A, list) end: A058562_list(18); # Peter Luschny, May 24 2017

MATHEMATICA

a[n_] := Sum[(n+k-1)!*Sum[1/(k-j)!*Sum[(3^(j-l)*(2)^l*(-1)^(l+j)* StirlingS1[n-l+j-1, j-l])/(l!*(n-l+j-1)!), {l, 0, j}], {j, 0, k}], {k, 0, n-1}]; Table[a[n], {n, 0, 17}] (* Jean-Fran├žois Alcover, Feb 26 2013, after Vladimir Kruchinin *)

PROG

(PARI) {a(n)=if(n<1, 0, n!*polcoeff(serreverse(3*log(1+x+x*O(x^n))-2*x), n))} \\ Paul D. Hanna, Aug 03 2008

(Maxima) a(n):=sum((n+k-1)!*sum(1/(k-j)!*sum((3^(j-l)*(2)^l*(-1)^(l+j)*stirling1(n-l+j-1, j-l))/(l!*(n-l+j-1)!), l, 0, j), j, 0, k), k, 0, n-1); \\ Vladimir Kruchinin, Sep 26 2012

CROSSREFS

Cf. A058540, A058371, A058575, A201465.

Sequence in context: A138903 A302703 A234855 * A145083 A234303 A138213

Adjacent sequences:  A058559 A058560 A058561 * A058563 A058564 A058565

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 26 2000

STATUS

approved

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Last modified November 14 12:38 EST 2019. Contains 329114 sequences. (Running on oeis4.)