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 A097171 Number of maximal matchings among labeled trees on n nodes. 4
 1, 1, 6, 24, 320, 3270, 55482, 999656, 21718440, 544829130, 15130478990, 475440344412, 16294653237876, 613546243029902, 25016884214147490, 1100408748640263120, 51948228453097163312, 2617775548597611727506, 140364712844785892810646, 7975414423897012183673540 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS S. Coulomb and M. Bauer, On vertex covers, matchings and random trees FORMULA Coulomb and Bauer give a g.f. MAPLE umax := 20 ; u := array(0..umax) ; U := proc() global umax, u ; local resul, n ; resul :=0 ; for n from 0 to umax do resul := resul+u[n]*x^n ; od: end: expU := proc() global umax, u ; taylor(exp(U()), x=0, umax+1) ; end: xexpU := proc() global umax, u ; taylor(x*expU(), x=0, umax+1) ; end: exexpU := proc() global umax, u ; local t ; t := xexpU() ; taylor(exp(-t^2+t+3*U()), x=0, umax+1) ; end: A := expand(taylor(U()-x^2*exexpU(), x=0, umax+1)) ; for n from 0 to umax do u[n] := solve(coeff(A, x, n), u[n]) ; od : F := proc() t := xexpU() ; taylor(-(t+U())^2/2+(1+U()*t)*t+U()-U()^2, x=0, umax+1) ; end: egf := F() ; for n from 1 to umax do n!*coeff(egf, x, n) ; od; # R. J. Mathar, Sep 14 2006 MATHEMATICA nmax = 20; egf := -U^2 - (1/2)*(E^U*x + U)^2 + E^U*x*(E^U*U*x + 1) + U; U = 1; Do[U = Normal[x^2*E^(E^(2U)*(-x^2) + E^U*x + 3U) + O[x]^n], {n, 1, nmax}]; Rest[Range[0, nmax - 1]!*CoefficientList[egf + O[x]^nmax, x]] (* Jean-François Alcover, Dec 14 2017 *) CROSSREFS Cf. A097170, A097172, A097173, A097174, A000169, A000272. Sequence in context: A052733 A323449 A010567 * A152886 A128614 A285018 Adjacent sequences:  A097168 A097169 A097170 * A097172 A097173 A097174 KEYWORD nonn AUTHOR Ralf Stephan, Jul 30 2004 EXTENSIONS More terms from R. J. Mathar, Sep 14 2006 STATUS approved

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Last modified February 21 06:40 EST 2019. Contains 320371 sequences. (Running on oeis4.)