OFFSET
1,7
COMMENTS
Achiral means that the polygon has an axis of reflective symmetry.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
FORMULA
PROG
(PARI)
Ro(n)=-(-1)^n + subst(serlaplace(polcoef(((1 - x)^2)/(2*(1 + x)*(1 + (1 - 2*y)*x + 2*y*x^2)) + O(x*x^n), n)), y, 1)
Re(n)=subst(serlaplace(polcoef((1 - 3*x)/(8*(1 + (1 - 2*y)*x + 2*y*x^2)) + O(x*x^n), n)), y, 1)
a(n) = if(n < 3, 0, if(n % 2, Ro(n\2), Re(n/2)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Mar 01 2024
STATUS
approved