OFFSET
3,5
LINKS
Eric Weisstein's World of Mathematics, Regular Polygon Division by Diagonals.
Index entries for linear recurrences with constant coefficients, signature (3,-1,-5,5,1,-3,1).
FORMULA
a(n) = 1/24*n*(n-4)*(n-6)*(2*n-7) for n even.
a(n) = 1/24*n*(n-3)*(n-5)*(2*n-11) for n odd.
G.f.: x^7*(2*x^2-3*x-7) / ((x-1)^5*(x+1)^2). [Colin Barker, Feb 14 2013]
MAPLE
a:= n-> `if`(n mod 2 = 0, 1/24*n*(n-4)*(n-6)*(2*n-7), 1/24*n*(n-3)*(n-5)*(2*n-11)): seq (a(n), n=3..40);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Martin Renner, Feb 07 2013
STATUS
approved