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A243214 Number of ways to place 5 points on a triangular grid of side n, so that no three of them are vertices of an equilateral triangle with sides parallel to the grid. 4

%I

%S 0,63,1566,13971,77124,319206,1083723,3181401,8344854,20006349,

%T 44548227,93248628,185176866,351410664,640972980,1129067352,

%U 1928196432,3203016813

%N Number of ways to place 5 points on a triangular grid of side n, so that no three of them are vertices of an equilateral triangle with sides parallel to the grid.

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

%Y Cf. A243211, A243210, A000217, A050534, A243212, A243213.

%K nonn,more

%O 3,2

%A _Heinrich Ludwig_, Jun 10 2014

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Last modified September 23 04:54 EDT 2020. Contains 337295 sequences. (Running on oeis4.)