OFFSET
0,4
COMMENTS
Also, the number of external intersections of the diagonals of a general n-gon = (A176145) - (A000332). - Michel Lagneau, Apr 21 2010
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: x^3*(3-x)/(1-x)^5. [Colin Barker, Jan 31 2012]
MAPLE
seq(n*(n-1)*(n-2)*(n+3)/12, n=0..40); # Wesley Ivan Hurt, Oct 10 2013
MATHEMATICA
Table[n(n-1)(n-2)(n+3)/12, {n, 0, 100}] (* Wesley Ivan Hurt, Sep 26 2013 *)
CoefficientList[Series[x^3 (3 - x)/(1 - x)^5, {x, 0, 80}], x] (* Vincenzo Librandi, Oct 10 2013 *)
PROG
(Magma) [n*(n-1)*(n-2)*(n+3)/12: n in [0..50]]; // Vincenzo Librandi, Oct 10 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Apr 11 2006
EXTENSIONS
Edited by N. J. A. Sloane, Apr 23 2006
STATUS
approved