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Search: id:A086365
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| A086365 |
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n-th Bell number of type D. A partition of {-n,...,-1,1,...,n} into nonempty subsets X_1,...,X_r is called `symmetric' if for each i -X_i = X_j for some j. a(n) is the number of such symmetric partitions such that none of the X_i are of the form {j,-j}. |
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+0
2
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| 1, 4, 15, 75, 428, 2781, 20093, 159340, 1372163, 12725447
(list; graph; listen)
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OFFSET
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0,2
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EXAMPLE
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a(2)=4 because the relevant partitions of {-2,-1,1,2} are {-2|-1|1|2}, {-2,-1|1,2}, {-2,1|-1,2} and {-2,-1,1,2}.
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CROSSREFS
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Cf. A002872, A086364.
Sequence in context: A039764 A020082 A020037 this_sequence A032270 A002750 A002467
Adjacent sequences: A086362 A086363 A086364 this_sequence A086366 A086367 A086368
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KEYWORD
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easy,nonn
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AUTHOR
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James East (jameseastseq(AT)hotmail.com), Sep 04 2003
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