OFFSET
3,4
COMMENTS
From the drawings as shown in links, it can be separated the distinct quadrilaterals into 3 types:
Q1: Quadrilaterals which have at least one side equal to n-gon sides length.
Q2: Quadrilaterals which have at least one pair parallel sides and all sides are longer than n-gon sides length.
Q3: Quadrilaterals which have no parallel sides and all sides are longer than n-gon side length.
LINKS
Kival Ngaokrajang, The distinct quadrilaterals for n = 4..9
Kival Ngaokrajang, The distinct quadrilaterals for n = 10
Kival Ngaokrajang, Q1 & Q2 for n = 23
Kival Ngaokrajang, Q3 for n = 23
FORMULA
Empirical g.f.: -x^4*(x^2-x+1)^2*(x^2+x+1) / ((x-1)^3*(x+1)*(x^2+1)). - Colin Barker, Oct 31 2013
EXAMPLE
For a pentagon, there are 5 quadrilaterals which are the same size and shape. Therefore a(5) = 1.
PROG
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Kival Ngaokrajang, May 25 2013
STATUS
approved