91171domain: NAppears in sequencesNumber of intersection points of all lines through pairs of vertices of a regular n-gon.at n=28A146212O.g.f.: Sum_{n>=0} 1/(1-n*x)^n * x^n/n! * exp(-x/(1-n*x)).at n=11A218667a(n) = (2*n+1)*(n^3-2*n^2+n+1).at n=15A347319