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 A050342 Expansion of Product_{m>=1} (1+x^m)^A000009(m). 22

%I

%S 1,1,1,3,4,7,12,19,30,49,77,119,186,286,438,670,1014,1528,2300,3437,

%T 5119,7603,11241,16564,24343,35650,52058,75820,110115,159510,230522,

%U 332324,477994,686044,982519,1404243,2003063,2851720,4052429,5748440,8140007,11507125

%N Expansion of Product_{m>=1} (1+x^m)^A000009(m).

%C Number of partitions of n into distinct parts with one level of parentheses. Each "part" in parentheses is distinct from all others at the same level. Thus (2+1)+(1) is allowed but (2)+(1+1) and (2+1+1) are not.

%H Alois P. Heinz, <a href="/A050342/b050342.txt">Table of n, a(n) for n = 0..1000</a>

%H N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>

%F Weigh transform of A000009.

%e 4=(4)=(3)+(1)=(3+1)=(2+1)+(1).

%e From _Gus Wiseman_, Oct 11 2018: (Start)

%e a(n) is the number of set systems (sets of sets) whose multiset union is an integer partition of n. For example, the a(1) = 1 through a(6) = 12 set systems are:

%e {{1}} {{2}} {{3}} {{4}} {{5}} {{6}}

%e {{1,2}} {{1,3}} {{1,4}} {{1,5}}

%e {{1},{2}} {{1},{3}} {{2,3}} {{2,4}}

%e {{1},{1,2}} {{1},{4}} {{1,2,3}}

%e {{2},{3}} {{1},{5}}

%e {{1},{1,3}} {{2},{4}}

%e {{2},{1,2}} {{1},{1,4}}

%e {{1},{2,3}}

%e {{2},{1,3}}

%e {{3},{1,2}}

%e {{1},{2},{3}}

%e {{1},{2},{1,2}}

%e (End)

%p g:= proc(n, i) option remember; `if`(n=0, 1,

%p `if`(i<1, 0, g(n, i-1)+`if`(i>n, 0, g(n-i, i-1))))

%p end:

%p b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,

%p add(binomial(g(i, i), j)*b(n-i*j, i-1), j=0..n/i)))

%p end:

%p a:= n-> b(n, n):

%p seq(a(n), n=0..50); # _Alois P. Heinz_, May 19 2013

%t g[n_, i_] := g[n, i] = If[n==0, 1, If[i<1, 0, g[n, i-1] + If[i>n, 0, g[n-i, i-1]]]]; b[n_, i_] := b[n, i] = If[n==0, 1, If[i<1, 0, Sum[Binomial[g[i, i], j]*b[n-i*j, i-1], {j, 0, n/i}]]]; a[n_] := b[n, n]; Table[a[n], {n, 0, 50}] (* _Jean-François Alcover_, Dec 19 2015, after _Alois P. Heinz_ *)

%t nn=10;Table[SeriesCoefficient[Product[(1+x^k)^PartitionsQ[k],{k,nn}],{x,0,n}],{n,0,nn}] (* _Gus Wiseman_, Oct 11 2018 *)

%Y Cf. A050343-A050350, A089254.

%Y Cf. A001970, A089259, A141268, A258466, A261049, A320328, A320330.

%K nonn

%O 0,4

%A _Christian G. Bower_, Oct 15 1999

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Last modified December 12 20:12 EST 2019. Contains 329961 sequences. (Running on oeis4.)