A240442 - OEIS

A240442

Number of ways to place 5 points on a triangular grid of side n so that no three of these points are vertices of an equilateral triangle of any orientation.

%I #11 Apr 25 2014 16:17:14

%S 0,39,1194,11259,64776,275805,957516,2859768,7606821,18444537,

%T 41458599,87464157,174846963,333687378,611613150,1081890447

%N Number of ways to place 5 points on a triangular grid of side n so that no three of these points are vertices of an equilateral triangle of any orientation.

%F a(n) = (n^10 + 5*n^9 - 30*n^8 - 150*n^7)/3840 + O(n^6).

%Y Cf. A240439, A240440, A240441.

%K nonn,more

%O 3,2

%A _Heinrich Ludwig_, Apr 08 2014

%E a(16)-a(18) from _Heinrich Ludwig_, Apr 25 2014