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Search: id:A108704
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| A108704 |
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Number of partitions of 112233...nn into n pairs. |
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+0
1
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| 1, 1, 4, 18, 126, 1110, 12120, 156660, 2341500, 39701340, 752839920, 15785181720, 362606123880, 9055825538760, 244296192460320, 7079382509799600, 219321853964413200, 7233629128601475600, 253054306933115688000
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OFFSET
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0,3
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REFERENCES
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Laszlo Lovasz: Combinatorial Problems and Solutions.
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FORMULA
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E.g.f.= exp(x*x/2)/sqrt(1-2*x)
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EXAMPLE
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Partitions of 1122 into 2 pairs: 11 22, 12 12, 12 21, 21 21 = 4 partitions so a(2)=4.
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MAPLE
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E(x):=exp(x*x/2)/sqrt(1-2*x): f[0]:=E(x): for n from 1 to 30 do f[n]:=diff(f[n-1], x) od: x:=0: seq(f[n], n=0..30);
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CROSSREFS
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Cf. A002135.
Sequence in context: A084661 A112294 A073511 this_sequence A001423 A158341 A144272
Adjacent sequences: A108701 A108702 A108703 this_sequence A108705 A108706 A108707
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KEYWORD
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nonn
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AUTHOR
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Miklos Kristof (kristmikl(AT)freemail.hu), Jun 20 2005
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