

A005646


Number of classifications of n elements.
(Formerly M2600)


8



1, 1, 1, 3, 6, 26, 122, 1015, 11847, 208914, 5236991, 184321511
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OFFSET

1,4


COMMENTS

"A 'classification' is a set of n typespecimens 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)


REFERENCES

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.


LINKS



EXAMPLE

Illustrated examples on Munafo web page.  Robert Munafo, Jan 24 2010


CROSSREFS



KEYWORD

nonn,nice,more


AUTHOR



EXTENSIONS

Erroneous "5236990" corrected to 5236991 by Robert Munafo, Jan 01 2010


STATUS

approved



