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 A273916 The Bingo-4 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. 1
 0, 4, 7, 9, 11, 12, 12, 14, 15, 16, 16, 18, 19, 20, 22, 24 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS You are permitted to put 5 or more adjacent stones in a line, but cannot count it as a group. Each pair of stones has at most one group that counts going through them. David A. Corneth, Aug 01 2016 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 lim_{n-> oo} a(n)/n = 1. See arXiv link. - Chai Wah Wu, Aug 25 2016 LINKS Hong-Chang Wang, Illustration of initial terms Chai Wah Wu, Minimal number of points on a grid forming patterns of blocks, arXiv:1608.07247 [math.CO], 2016 EXAMPLE From M. F. Hasler, Jul 30 2016: (Start) One can get n=3 groups using a(3) = 9 stones (O) as follows:    O O O O     The 3 groups are:    . O O .     (1) the first line,    . O . .     (2) the second column,    O O . .     (3) the antidiagonal. See the link for more examples. (End) CROSSREFS See also the 4-trees-in-a-row orchard problem, A006065. Sequence in context: A272015 A310941 A310942 * A053169 A007656 A159619 Adjacent sequences:  A273913 A273914 A273915 * A273917 A273918 A273919 KEYWORD nonn,more,nice AUTHOR Jiangshan Sun, Jason Y.S. Chiu, Hong-Chang Wang, Jun 03 2016 EXTENSIONS Edited by N. J. A. Sloane, Jul 29 2016 STATUS approved

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Last modified October 18 12:18 EDT 2019. Contains 328160 sequences. (Running on oeis4.)