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 A052855 Number of forests of rooted trees of nonempty sets with n points. (Each node is a set of 1 or more points.) 4
 1, 1, 3, 8, 24, 71, 224, 710, 2318, 7659, 25703, 87153, 298574, 1031104, 3587263, 12558652, 44214807, 156438309, 555973965, 1983817178, 7104313970, 25525304569, 91986529421, 332408847422, 1204259931815, 4373027942634, 15914143511582, 58030451159889 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Euler transform of A036249 (as well as first differences thereof). - Franklin T. Adams-Watters, Feb 08 2006 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..1717 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 823 FORMULA G.f. satisfies: A(x) = exp( Sum_{n>=1} A(x^n)/(1-x^n) * x^n/n  ). [From Paul D. Hanna, Oct 26 2011] MAPLE spec := [S, {B=Sequence(Z, 1 <= card), S=Set(C), C=Prod(B, S)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA max = 26; A[_] = 1; Do[A[x_] = Exp[Sum[A[x^k]/(1 - x^k)*x^k/k + O[x]^n, {k, 1, n}]] // Normal, {n, 1, max}]; CoefficientList[A[x] + O[x]^max, x] (* Jean-François Alcover, May 25 2018 *) PROG (PARI) {a(n)=local(A=1+x); for(i=1, n, A=exp(sum(m=1, n, subst(A/(1-x), x, x^m+x*O(x^n))*x^m/m))); polcoeff(A, n)} /* Paul D. Hanna */ CROSSREFS First differences of A036249 and A029856. Sequence in context: A027077 A291243 A153774 * A133787 A080923 A118264 Adjacent sequences:  A052852 A052853 A052854 * A052856 A052857 A052858 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 EXTENSIONS More terms from Franklin T. Adams-Watters, Feb 08 2006 STATUS approved

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Last modified November 27 14:10 EST 2020. Contains 338683 sequences. (Running on oeis4.)