1,4

"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".

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.

P. J. Wexler and D. H. Fremlin, The number of classifications of up to seven classificands, Classification Society Bull., 4 (No. 3, 1979), 2-4.

Sequence in context: A148665 A148666 A058258 this_sequence A033194 A128437 A064283

Adjacent sequences: A005643 A005644 A005645 this_sequence A005647 A005648 A005649

nonn,nice,more

N. J. A. Sloane (njas(AT)research.att.com).