OFFSET
1,3
COMMENTS
If Y is a 3-subset of an 2n-set X then, for n>=6, a(n+1) is the number of 3-subsets of X having at least two elements in common with Y. - Milan Janjic, Dec 16 2007
REFERENCES
L. W. Beineke, Biplanar graphs: a survey, Computers Math. Applic., 34 (1997), 1-8.
Hutchinson, Joan P.; Shermer, Thomas; and Vince, Andrew; On representations of some thickness-two graphs. Comput. Geom. 13 (1999), 161-171.
FORMULA
If n <= 8 then n*(n-1)/2 else 6*n-20.
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 02 2006
STATUS
approved