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A195912
Number of proper (n,3)-clusterings.
0
1, 38, 675, 7840, 74291, 630546, 5014843, 38290580, 284670771, 2078666854, 14991726971, 107192696520, 761785678291, 5390429149562, 38025671502459, 267655258816060, 1881013969942451, 13204432684440270
OFFSET
3,2
COMMENTS
See Roman et al. for precise definition.
LINKS
Adam Roman, Igor T. Podolak and Agnieszka Deszynska, On the number of clusterings in a hierarchical classification model with overlapping clusters, Schedae Informaticae, Volume 20, 2011.
FORMULA
Roman et al. give an explicit formula.
PROG
(PARI) a(n) = {if (n==3, return (1)); n --; return (7*a(n) + 2*5^n - 3*4^n + (4*n-11)*3^n/6 + (4 - 15*n/4)*2^n + 9*n - 1/2); } \\ Michel Marcus, Apr 21 2013
CROSSREFS
Sequence in context: A094034 A020931 A089271 * A240425 A269010 A010954
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 06 2012
EXTENSIONS
More terms from Michel Marcus, Apr 21 2013
STATUS
approved