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A052816
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G.f.: (1+x)*Product_{m>0} (1 + x^m).
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1
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1, 2, 2, 3, 4, 5, 7, 9, 11, 14, 18, 22, 27, 33, 40, 49, 59, 70, 84, 100, 118, 140, 165, 193, 226, 264, 307, 357, 414, 478, 552, 636, 730, 838, 960, 1097, 1253, 1428, 1624, 1846, 2095, 2373, 2686, 3036, 3426, 3864, 4352, 4894, 5500, 6174, 6922, 7755, 8679, 9702
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 781
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FORMULA
| G.f.: exp(Sum((-1)^(j[1]+1)*x^j[1]*(x^j[1]-2)/(x^j[1]-1)/j[1], j[1]=1 .. infinity))
a(n) = A000009(n) + A000009(n-1). - Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 23 2003
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Union(B, Z), S=PowerSet(C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A134727 A152305 A131419 * A122130 A003073 A123946
Adjacent sequences: A052813 A052814 A052815 * A052817 A052818 A052819
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 23 2003
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