OFFSET
1,5
COMMENTS
Also, number of chord configurations on n vertices of the period n.
Number of such chord configurations on 2n vertices with n chords is given by A005354(n+1).
EXAMPLE
For n=2, there are only two configurations possible: two diametrically located points on a circle connected or not connected with a chord. Since both these configurations are invariant w.r.t. rotation by angle Pi, a(2)=0.
CROSSREFS
KEYWORD
nonn
AUTHOR
Max Alekseyev, Oct 29 2010
STATUS
approved