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 A052805 If B is a collection in which there are C(n-1) [Catalan numbers, A000108] things with n points, a(n) is the number of subsets without repetition of B with a total of n points. 2
 1, 1, 1, 3, 7, 21, 64, 204, 666, 2236, 7625, 26419, 92644, 328370, 1174234, 4231898, 15354424, 56042372, 205626906, 758021598, 2806143522, 10427671924, 38882984840, 145443260702, 545598228056, 2052086677666, 7736986142773, 29236241424977 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Euler transform of sequence [1,0,2,4,14,40,132,424,1430,...] (C(n-1) if n odd, C(n-1)-C(n/2-1) if n even). LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 766 FORMULA a(n)=(1/n)*Sum_{k=1..n} a(n-k)*b(k), n>0, a(0)=1, b(k)=Sum_{d|k} (-1)^(k/d+1)*binomial(2*d-2, d-1). - Vladeta Jovovic, Jan 17 2002 G.f. A(x)=exp(Sum_{k>0} -(-1)^k* C(x^k)/k) where C(x)=(1-sqrt(1-4x))/2= g.f. A000108 (offset 1). G.f.: Product_{k>=1} (1+x^k)^(1/k*binomial(2*k-2, k-1)). - Vladeta Jovovic, Jan 17 2002 MAPLE spec := [S, {C=Sequence(B), B=Prod(C, Z), S=PowerSet(B)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA ClearAll[a]; b[k_] := Sum[ (-1)^(k/d + 1)*Binomial[2*d - 2, d - 1], {d, Divisors[k]}]; a[0] = 1; a[n_] := a[n] = (1/n)*Sum[a[n - k]*b[k], {k, 1, n}]; Table[a[n], {n, 0, 27}] (* Jean-François Alcover, Oct 08 2012, after Vladeta Jovovic *) PROG (PARI) a(n)=local(A); if(n<1, !n, A=sum(k=1, n, (2*k-2)!/k!/(k-1)!*x^k, x*O(x^n)); polcoeff(exp(sum(k=1, n, -(-1)^k*subst(A, x, x^k)/k)), n)) CROSSREFS Cf. A000108, A052854. Sequence in context: A151412 A121797 A109361 * A148674 A148675 A148676 Adjacent sequences:  A052802 A052803 A052804 * A052806 A052807 A052808 KEYWORD easy,nonn,nice AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified May 26 20:51 EDT 2022. Contains 354092 sequences. (Running on oeis4.)