OFFSET
1,1
COMMENTS
A transitive relation is vacuously transitive if it does not contain any transitive triple, that is, three distinct ordered pairs (a,b), (b,c), (a,c). - Jukka Kohonen, Sep 17 2021
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
H. Sharp, Jr., Enumeration of vacuously transitive relations, Discrete Math. 4 (1973), 185-196.
EXAMPLE
a(2)=7: The seven relations are {}, {(1,1)}, {(1,1),(2,2)}, {(2,1)}, {(1,1),(2,1)}, {(1,1),(2,1),(2,2)} and {(2,1),(2,2)}. - Jukka Kohonen, Sep 17 2021
CROSSREFS
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
Clarified and offset corrected by Jukka Kohonen, Sep 17 2021
STATUS
approved