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 A066399 From reversion of e.g.f. for squares. 2
 0, 1, -4, 39, -616, 13505, -379296, 12995983, -525688192, 24519144609, -1295527513600, 76481653648631, -4989249262503936, 356408413864589281, -27670449142629400576, 2319870547729387929375, -208886312501433616531456, 20104397299878424990749377 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Robert Israel, Table of n, a(n) for n = 0..300 Vladimir Kruchinin, The method for obtaining expressions for coefficients of reverse generating functions, arXiv:1211.3244 [math.CO], 2012. FORMULA a(n+1) = (-1)^n*(n)! * Sum_{m=0..n} (n+1)^m/m! * binomial(2*n-m,n). - Vladimir Kruchinin, Feb 22 2011 For n>=2, a(n) = (-2)^(n-1)*(2n-3)!!*hypergeom([1-n], [2-2n], n), where n!! denotes the double factorial A006882. - Vladimir Reshetnikov, Oct 16 2015 E.g.f. g(x) satisfies (g(x) + g(x)^2)*exp(g(x)) = x. - Robert Israel, Oct 16 2015 a(n) ~ (-1)^(n-1) * (2 + sqrt(5))^(n-1/2) * n^(n-1) / (5^(1/4) * exp((sqrt(5) - 1)*n/2)). - Vaclav Kotesovec, Oct 18 2015 MAPLE read transforms; add(n^2*x^n/n!, n=1..30); series(%, x, 31): seriestoseries(%, 'revogf'); SERIESTOLISTMULT(%); with(powseries):powcreate(t(n)=n^2/n!):seq(n!*coeff(tpsform(reversion(t), x, 19), x, n), n=0..18); spec:=[A, {A=Prod(Z, Set(A), Set(B)), B=Cycle(A)}, labeled]; seq(combstruct[count](spec, size=n), n=0..18); # Vladeta Jovovic, May 29 2007 a := n -> `if`(n<2, n, (-2)^(n-1)*doublefactorial(2*n-3)*hypergeom([1-n], [2-2*n], n)): seq(simplify(a(n)), n=0..18); # Peter Luschny, Oct 16 2015 MATHEMATICA A066399[0] = 0; A066399[1] = 1; A066399[n_] := (-2)^(n - 1) (2 n - 3)!! Hypergeometric1F1[1 - n, 2 - 2 n, n]; Table[A066399[n], {n, 0, 10}] (* Vladimir Reshetnikov, Oct 16 2015 *) PROG (PARI) a(n) = if(n==0, 0, (-1)^(n-1)*(n-1)! * sum(k=0, n-1, (n)^k/k! * binomial(2*n-2-k, n-1))) \\ Altug Alkan, Oct 16 2015 CROSSREFS Cf. A295188. Sequence in context: A024055 A189489 A178920 * A065760 A132612 A129463 Adjacent sequences:  A066396 A066397 A066398 * A066400 A066401 A066402 KEYWORD sign AUTHOR N. J. A. Sloane, Dec 25 2001 STATUS approved

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Last modified September 17 22:53 EDT 2019. Contains 327147 sequences. (Running on oeis4.)