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A001173 Relations on n unlabeled points.
(Formerly M4010 N1662)
5
1, 5, 52, 1522, 145984, 48464496, 56141454464, 229148550030864, 3333310786076963968, 174695272746749919580928, 33301710992539090379269318144, 23278728241293494533015563325552128 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

R. L Davis, The number of structures of finite relations, Proc. Amer. Math. Soc. 4 (1953), 486-495.

M. D. McIlroy, Calculation of numbers of structures of relations on finite sets, Massachusetts Institute of Technology, Research Laboratory of Electronics, Quarterly Progress Reports, No. 17, Sept. 15, 1955, pp. 14-22.

W. Oberschelp, Kombinatorische Anzahlbestimmungen in Relationen, Math. Ann., 174 (1967), 53-78.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=1..12.

M. D. McIlroy, Calculation of numbers of structures of relations on finite sets, Massachusetts Institute of Technology, Research Laboratory of Electronics, Quarterly Progress Reports, No. 17, Sep. 15, 1955, pp. 14-22. [Annotated scanned copy]

FORMULA

a(n) = A000595(n)/2. - Sean A. Irvine, Mar 16 2012

CROSSREFS

Cf. A000595, A001174.

Sequence in context: A278879 A216464 A279644 * A277202 A223248 A208303

Adjacent sequences:  A001170 A001171 A001172 * A001174 A001175 A001176

KEYWORD

nonn,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Vladeta Jovovic, Apr 18 2000

STATUS

approved

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Last modified December 10 09:49 EST 2018. Contains 318047 sequences. (Running on oeis4.)