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 A101053 a(n) = n!*Sum_{k=0..n} Bell(k)/k! (cf. A000110). 6

%I

%S 1,2,6,23,107,587,3725,26952,219756,1998951,20105485,221838905,

%T 2666280457,34689290378,485840964614,7288997427755,116634438986227,

%U 1982868327635663,35692311974248093,678159760252918824,13563246929216611852,284828660383365005643

%N a(n) = n!*Sum_{k=0..n} Bell(k)/k! (cf. A000110).

%C Sequence was originally defined as an infinite sum involving generalized Laguerre polynomials: a(n)= ((-1)^n*n!/exp(1))*Sum_{k>=0} LaguerreL(n,-n-1,k)/k!, n=0,1... . It appears in the problem of normal ordering of functions of boson operators.

%C a(n) is the number of ways to linearly order the elements in a (possibly empty) subset S of {1,2,...,n} and then partition the complement of S. - _Geoffrey Critzer_, Aug 07 2015

%H Robert Israel, <a href="/A101053/b101053.txt">Table of n, a(n) for n = 0..450</a>

%F E.g.f: exp(exp(x)-1)/(1-x).

%p with(combinat): a:=n->add(bell(j)*n!/j!,j=0..n): seq(a(n),n=0..20); # _Zerinvary Lajos_, Mar 19 2007

%t nn = 21; Range[0, nn]! CoefficientList[Series[Exp[(Exp[x]-1)]/(1-x), {x, 0, nn}], x] (* _Geoffrey Critzer_, Aug 07 2015 *)

%o (PARI) egf(s)=my(v=Vec(s),i); while(polcoeff(s,i)==0,i++); i--; vector(i+#v,j,polcoeff(s,j+i)*(j+i)!)

%o egf(exp(exp(x)-1)/(1-x)) \\ _Charles R Greathouse IV_, Aug 07 2015

%o (PARI) my(x='x+O('x^30)); Vec(serlaplace( exp(exp(x)-1)/(1-x) )) \\ _G. C. Greubel_, Mar 31 2019

%o (MAGMA) m:=30; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!( Exp(Exp(x)-1)/(1-x) )); [Factorial(n-1)*b[n]: n in [1..m]]; // _G. C. Greubel_, Mar 31 2019

%o (Sage) m = 30; T = taylor(exp(exp(x)-1)/(1-x), x, 0, m); [factorial(n)*T.coefficient(x, n) for n in (0..m)] # _G. C. Greubel_, Mar 31 2019

%Y Cf. A000110.

%K nonn

%O 0,2

%A _Karol A. Penson_, Nov 29 2004

%E New definition from _Vladeta Jovovic_, Dec 01 2004

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Last modified December 5 23:39 EST 2019. Contains 329784 sequences. (Running on oeis4.)