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 A071379 a(n) = (1/e) * Sum_{k>=0} ((k+4)!/k!)^(n-1)/k!. 8
 1, 1, 209, 163121, 326922081, 1346634725665, 9939316337679281, 119802044788535500753, 2205421644124274191535553, 58945667435045762187763602753, 2198513228897522394476415669503377, 110833342180980170285766876408530089329 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS This is a Dobinski-type summation formula. Terms quickly become gigantic: a(15) = 9142140479823239889945170786704021785456107245847570873873. a(n) appears in the process of ordering the n-th power of a product of fourth power of boson creation and fourth power of boson annihilation operators. From Peter Luschny, Mar 27 2011: (Start) Let B_{m}(x) = Sum_{j>=0} (exp(j!/(j-m)!*x-1)/j!) then a(n) = n! [x^n] Taylor(B_{4}(x)), where [x^n] denotes the coefficient of x^k in the Taylor series for B_{4}(x). a(n) is row 4 of the square array representation of A090210. (End) LINKS P. Blasiak, K. A. Penson and A. I. Solomon, The general boson normal ordering problem, arXiv:quant-ph/0402027, 2004. P. Blasiak, K. A. Penson and A. I. Solomon, The general boson normal ordering problem/a>, Phys. Lett. A 309 (2003) 198-205. K. A. Penson, P. Blasiak, A. Horzela, A. I. Solomon and G. H. E. Duchamp, Laguerre-type derivatives: Dobinski relations and combinatorial identities, J. Math. Phys. 50, 083512 (2009). M. Schork, On the combinatorics of normal ordering bosonic operators and deforming it, J. Phys. A 36 (2003) 4651-4665. FORMULA a(n) = (1/e)*Sum_{k>=4} fallfac(k, 4)^n / k!, n >= 1, with fallfac(n, m) := A008279(n, m) (falling factorials). (From eq.(26) with r=4 of the Schork reference.) E.g.f. with a(0) := 1: (1/e)*(Sum_{k>=4} e^(fallfac(k, 4)*x)/k! + 8/3). From top of p. 4656 with r=4 of the Schork reference. MAPLE A071379 := proc(n) local r, s, i; if n=0 then 1 else r := [seq(5, i=1..n-1)]; s := [seq(1, i=1..n-1)]; exp(-x)*24^(n-1)*hypergeom(r, s, x); round(evalf(subs(x=1, %), 99)) fi end: seq(A071379(n), n=0..10); # Peter Luschny, Mar 30, 2011 MATHEMATICA a[n_] := Sum[FactorialPower[k, 4]^n/k!, {k, 4, Infinity}]/E; a = 1; Array[a, 12, 0] (* Jean-François Alcover, Sep 01 2016 *) PROG (PARI) default(realprecision, 500); for(n=0, 20, print1(if(n==0, 1, round(exp(-1)*sum(k=0, 500, ((k+4)!/k!)^(n-1)/k!))), ", ")) \\ G. C. Greubel, May 15 2018 CROSSREFS Cf. A000110, A020556 and A069223, when k+4 is replaced by k+1, k+2 or k+3 respectively. Cf. A090210. Sequence in context: A003779 A268659 A265682 * A283153 A125549 A104876 Adjacent sequences:  A071376 A071377 A071378 * A071380 A071381 A071382 KEYWORD nonn AUTHOR Karol A. Penson, May 22 2002 EXTENSIONS a(0)=1 prepended by Alois P. Heinz, Aug 01 2016 If it is proved that A283153 and A071379 are the same, then the entries should be merged and A283153 recycled. - N. J. A. Sloane, Mar 06 2017 STATUS approved

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Last modified February 23 06:13 EST 2020. Contains 332159 sequences. (Running on oeis4.)