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%I M2600 #21 Jun 17 2022 14:45:32
%S 1,1,1,3,6,26,122,1015,11847,208914,5236991,184321511
%N Number of classifications of n elements.
%C "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".
%C From _Robert Munafo_, Jan 24 2010: (Start)
%C Extensive explanation with illustrations on Munafo web page.
%C This sequence gives the row sums of triangle A171871. (End)
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%D P. J. Wexler, On the number of taxonomies; or the odds on 'structuralism', American Anthropologist, 73 (1971), 1258.
%H Robert Munafo, <a href="http://mrob.com/pub/math/seq-a005646.html">Web page about this sequence (with additional terms)</a> [Added Jan 04 2010]
%H P. J. Wexler and D. H. Fremlin, <a href="/A005646/a005646.pdf">The number of classifications of up to seven classificanda</a>, Classification Society Bull., 4 (No. 3, 1979), 2-4. (Annotated scanned copy)
%e Illustrated examples on Munafo web page. - _Robert Munafo_, Jan 24 2010
%Y Cf. A000055, A171872, A171873. - _Robert Munafo_, Jan 24 2010
%K nonn,nice,more
%O 1,4
%A _N. J. A. Sloane_
%E 1015 term first calculated by _Andrew Weimholt_, Dec 15 2009
%E 11847 term first calculated by _Andrew Weimholt_, Dec 19 2009
%E 208914 term first calculated by _Robert Munafo_, Dec 29 2009
%E 5236990 term (erroneous) from _Robert Munafo_, Dec 30 2009
%E Erroneous "5236990" corrected to 5236991 by _Robert Munafo_, Jan 01 2010
%E 184321511 term first calculated by _Robert Munafo_, Jan 10 2010
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