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 A038052 Number of labeled trees of nonempty sets with n points. (Each node is a set of 1 or more points.) 7
 1, 1, 2, 7, 42, 376, 4513, 68090, 1238968, 26416729, 646140364, 17837852044, 548713088399, 18612963873492, 690271321314292, 27785827303491579, 1206582732097720126, 56224025231569020724, 2798445211000659147033 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS T. D. Noe, Table of n, a(n) for n = 0..100 FORMULA E.g.f.: B(e^x-1) where B is e.g.f. of A000272. a(n) = Sum_{k=1..n} Stirling2(n, k)*k^(k-2). - Vladeta Jovovic, Sep 20 2003 a(n) ~ (1+exp(1))^(3/2) * n^(n-2) / (exp(n) * (log(1+exp(-1)))^(n-3/2)). - Vaclav Kotesovec, Feb 17 2017 MATHEMATICA a[0] = 1; a[n_] := Sum[StirlingS2[n, k]*k^(k - 2), {k, 1, n}]; Table[a[n], {n, 0, 18}] (* Jean-François Alcover, Sep 09 2013, after Vladeta Jovovic *) CROSSREFS Cf. A036250, A048802. Sequence in context: A131682 A317349 A158840 * A066383 A011802 A007065 Adjacent sequences:  A038049 A038050 A038051 * A038053 A038054 A038055 KEYWORD nonn,nice,easy AUTHOR Christian G. Bower, Jan 04 1999 STATUS approved

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Last modified January 22 19:00 EST 2019. Contains 319365 sequences. (Running on oeis4.)