

A175716


The total number of elements(ordered pairs) in all equivalence relations on {1,2,...,n}


1



0, 1, 6, 27, 120, 560, 2778, 14665, 82232, 488403, 3062980, 20221520, 140134404, 1016698813, 7703878042, 60833235795, 499592325152, 4259301450652, 37634032670886, 344092369602461, 3250925202629100
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OFFSET

0,3


LINKS

Table of n, a(n) for n=0..20.


FORMULA

a(n) = n*A124427(n).  Joerg Arndt, Dec 04 2010.
E.g.f.: (x+x^2) * exp(x) * exp(exp(x)1).


EXAMPLE

a(2)= 6 because the equivalence relations on {1,2}: {(1,1), (2,2)}, {(1,1), (2,2), (1,2), (2,1)} contain 6 ordered pairs.


MATHEMATICA

f[list_] := Length[list]^2; Table[Total[Map[f, Level[SetParttions[n], {2}]]], {n, 0, 12}] (* or *)
Range[0, 20]! CoefficientList[Series[(x + x^2)Exp[x] * Exp[Exp[x]  1], {x, 0, 20}], x]


CROSSREFS

Cf. A124427, A000595.
Sequence in context: A080620 A080627 A079762 * A178935 A249792 A002912
Adjacent sequences: A175713 A175714 A175715 * A175717 A175718 A175719


KEYWORD

nonn


AUTHOR

Geoffrey Critzer, Dec 04 2010


STATUS

approved



