%I
%S 0,4,7,9,11,12,12,14,15,16,16,18,19,20,22,24
%N The Bingo4 problem: minimal number of stones that must be placed on an infinite square grid to produce n groups of exactly 4 stones each. Groups consist of adjacent stones in a horizontal, vertical or diagonal line.
%C You are permitted to put 5 or more adjacent stones in a line, but cannot count it as a group.
%C Each pair of stones has at most one group that counts going through them. _David A. Corneth_, Aug 01 2016
%C a(n) >= n and a(n+m) <= a(n)+a(m), i.e., a(16) <= a(10)+a(6) = 28. Placing stones in a 4 X k rectangular array shows that a(3k) <= 4(k+2). Fekete's subadditive lemma shows that 1 <= lim_{n> oo} a(n)/n <= 4/3 exists.  _Chai Wah Wu_, Jul 31 2016
%C lim_{n> oo} a(n)/n = 1. See arXiv link.  _Chai Wah Wu_, Aug 25 2016
%H HongChang Wang, <a href="/A273916/a273916.png">Illustration of initial terms</a>
%H Chai Wah Wu, <a href="http://arxiv.org/abs/1608.07247">Minimal number of points on a grid forming patterns of blocks</a>, arXiv:1608.07247 [math.CO], 2016
%e From _M. F. Hasler_, Jul 30 2016: (Start)
%e One can get n=3 groups using a(3) = 9 stones (O) as follows:
%e O O O O The 3 groups are:
%e . O O . (1) the first line,
%e . O . . (2) the second column,
%e O O . . (3) the antidiagonal.
%e See the link for more examples. (End)
%Y See also the 4treesinarow orchard problem, A006065.
%K nonn,more,nice
%O 0,2
%A _Jiangshan Sun_, _Jason Y.S. Chiu_, _HongChang Wang_, Jun 03 2016
%E Edited by _N. J. A. Sloane_, Jul 29 2016
