11044215domain: NAppears in sequencesNumber of ways to place 3 points on a triangular grid of side n so that they are not vertices of an equilateral triangle of any orientation.at n=27A240440a(n) = Sum_{k=0..floor(n/4)} binomial(n+k-1,k) * binomial(k,n-4*k).at n=26A389291