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A005646
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Number of classifications of n elements.
(Formerly M2600)
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8
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1, 1, 1, 3, 6, 26, 122, 1015, 11847, 208914, 5236991, 184321511
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listen;
history;
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OFFSET
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1,4
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COMMENTS
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"A 'classification' is a set of n type-specimens each one of which is corralled on its own by the union of a set of binary partitions, none of which could be omitted without leaving 2 types unseparated".
Extensive explanation with illustrations on Munafo web page.
This sequence gives the row sums of triangle A171871. (End)
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
P. J. Wexler, On the number of taxonomies; or the odds on 'structuralism', American Anthropologist, 73 (1971), 1258.
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LINKS
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EXAMPLE
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Illustrated examples on Munafo web page. - Robert Munafo, Jan 24 2010
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CROSSREFS
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KEYWORD
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nonn,nice,more
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AUTHOR
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EXTENSIONS
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Erroneous "5236990" corrected to 5236991 by Robert Munafo, Jan 01 2010
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STATUS
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approved
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